Communication apparatus and communication method in wireless power transmission system

ABSTRACT

An apparatus and method for performing communication in a wireless power transmission system are provided. The apparatus includes a channel search unit configured to search for communication channels other than a channel used in wireless power transmission, and measure state information of the communication channels. The apparatus includes a channel determining unit configured to determine a communication channel available for communication with a target device based on the measured state information. The apparatus includes a communication unit configured to transmit an access instruction to the target device using the determined communication channel. The apparatus includes a controller configured to determine whether to communicate with the target device using the determined communication channel based on whether a response signal corresponding to the access instruction is received.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 10-2011-0089396, filed on Sep. 5, 2011, andKorean Patent Application No. 10-2011-0110531, filed on Oct. 27, 2011,in the Korean Intellectual Property Office, the entire disclosures ofwhich are each incorporated herein by reference for all purposes.

BACKGROUND

1. Field

The following description relates to an apparatus and method forperforming communication in a wireless power transmission system.

2. Description of Related Art

Research on wireless power transmission have been started to overcomethe increasing inconvenience of wired power supplies, and the limitedcapacity of conventional batteries, due to the increasing number ofvarious electronic devices including electric vehicles and mobiledevices. One wireless power transmission technology uses resonancecharacteristics of radio frequency (RF) devices.

For example, a wireless power transmission system using resonancecharacteristics may include a source device configured to supply apower, and a target device configured to receive supplied power. Toefficiently transmit power from the source device to the target device,the source device and the target device may need to exchange informationon a state of the source device, and information on a state of thetarget device, with each other. In other words, there is a demand toperform communication between the source device and the target device.

SUMMARY

In one general aspect, there is provided a communication apparatus in awireless power transmission system, the communication apparatusincluding a channel search unit configured to search for communicationchannels other than a channel used in wireless power transmission, andmeasure state information of the communication channels. Thecommunication apparatus further includes a channel determining unitconfigured to determine a communication channel available forcommunication with a target device based on the measured stateinformation. The communication apparatus further includes acommunication unit configured to transmit an access instruction to thetarget device using the determined communication channel. Thecommunication apparatus further includes a controller configured todetermine whether to communicate with the target device using thedetermined communication channel based on whether a response signalcorresponding to the access instruction is received.

The communication apparatus may be configured to detect the targetdevice in a wireless power transmission region of the communicationapparatus.

The channel search unit may include a channel measuring unit configuredto measure intensities of interference signals of the respectivecommunication channels.

The channel measuring unit may be further configured to measure theintensities for a predetermined period of time.

The channel determining unit may be further configured to determine acommunication channel including an intensity of an interference signalthat is less than or equal to a predetermined value, among the measuredintensities, to be the communication channel available for communicationwith the target device.

The channel determining unit may be further configured to determine acommunication channel including an intensity of an interference signalthat is lowest in value, among the measured intensities, to be thecommunication channel available for communication with the target deviceif each of the intensities are greater than or equal to a channelselection reference level.

The communication unit may be further configured to transmit a channelseizure signal to the target device, the channel seizure signalincluding a predetermined intensity.

The channel seizure signal may be a continuous wave (CW) signalincluding a predetermined intensity and a power greater than acommunication signal of a direct-sequence spread spectrum (DSSS).

The controller may be further configured to assign a control identifier(ID) to the target device if the response signal is received.

The communication unit may be further configured to transmit a signal torequest information on a power required by the target device using acommunication frequency of the determined communication channel.

The controller may be further configured to determine an amount of awireless power to be transmitted by the communication apparatus based onthe information regarding the power required by the target device. Thecontroller may be further configured to control a wireless power outputfrom the communication apparatus based on the determined amount of thewireless power.

The channel search unit may be further configured to search for thecommunication channels based on a search table set based on a type ofthe communication apparatus, or a unique ID assigned to thecommunication apparatus.

The controller may be further configured to control the channel searchunit to search for the communication channels, regardless of whether thetarget device is waked up.

The controller may be further configured to determine whether thecommunication apparatus is accessed by the target device based oninformation on a power of a communication output of the communicationapparatus in the determined communication channel, and information on apower of the communication output received by the target device.

The controller may be further configured to control the channel searchunit to search for the communication channels based on a channel searchstart command if the communication apparatus is not accessed by thetarget device. The controller may be further configured to control thechannel search unit to search for the communication channels based on anamount of a change in a current output from the communication apparatusif the communication apparatus is accessed by the target device.

The controller may be further configured to determine a differencebetween a wireless power transmitted by the communication apparatus anda power transferred to a load of the target device. The controller maybe further configured to determine whether the target device incorrectlyaccesses the communication apparatus based on the determined difference.

The controller may be further configured to determine a differencebetween a time in which an amount of a wireless power transmitted by thecommunication apparatus is changed to a predetermined value, and a timein which an amount of a power transferred to a load of the target deviceis changed. The controller may be further configured to determinewhether the target device incorrectly accesses the communicationapparatus based on the determined difference.

The controller may be further configured to determine a power of acommunication output in the determined communication channel based on atable to which an intensity of an interference signal in the determinedcommunication channel, and a power of an output signal required totransmit data within a predetermined error range, are mapped.

The controller may be further configured to determine a time required tomeasure intensities of interference signals of the respectivecommunication channels.

The controller may be further configured to determine to change thedetermined communication channel to another communication channel if anerror in the determined communication channel between the communicationapparatus and the target device is greater than a predetermined value,or if an intensity of an interference signal of the determinedcommunication channel is greater than a predetermined value. Thecontroller may be further configured to transmit a channel changerequest instruction to the target device.

In another general aspect, there is provided a communication apparatusin a wireless power transmission system, the communication apparatusincluding a channel search unit configured to search for communicationchannels other than a channel used in wireless power transmission, andmeasure state information of the communication channels. Thecommunication apparatus further includes a channel determining unitconfigured to determine a communication channel available forcommunication with a source device based on the measured stateinformation. The communication apparatus further includes a controllerconfigured to determine whether to communicate with the source deviceusing the determined communication channel based on whether an accessinstruction is received from the source device using the determinedcommunication channel.

The controller may be further configured to determine whether the accessinstruction is received from the source device using the determinedcommunication channel within a reference time.

The communication apparatus may further include a communication unitconfigured to transmit, to the source device, a response signalcorresponding to the access instruction if the access instruction isreceived within the reference time.

The communication unit may be further configured to receive, from thesource device, a control ID assigned to the communication apparatus andthat corresponds to the response signal.

The channel search unit may be further configured to search for anothercommunication channel, and measure state information of the othercommunication channel, if the access instruction is not received withinthe reference time.

The channel search unit may be further configured to measure intensitiesof channel seizure signals of the respective communication channels thatare transmitted by the source device. The channel determining unit maybe further configured to determine a communication channel including anintensity of a channel seizure signal that is greater than apredetermined value, among the intensities, to be the communicationchannel available for communication with the source device.

The communication apparatus may be configured to receive channel seizuresignals from source devices. The controller may be further configured toselect one of the source devices using a communication channel includingan intensity of a channel seizure signal that is greatest in value, fromamong the source devices, and determine to receive a wireless power fromthe selected one of the source devices.

The channel determining unit may be further configured to determine thecommunication channel used by the selected one of the source devices tobe a communication channel available for communication with the selectedone of the source devices.

The channel search unit may be further configured to search for thecommunication channels based on a search table set based on a type ofthe communication apparatus, or a unique ID assigned to thecommunication apparatus.

The communication apparatus may further include a direct current(DC)-to-DC (DC/DC) converter. The communication apparatus may furtherinclude a load. The controller may be further configured to determine apower required by the communication apparatus based on a power measuredat an input end of the DC/DC converter, a power measured at an outputend of the DC/DC converter, and a power transferred to the load.

In still another general aspect, there is provided a communicationmethod in a wireless power transmission system, the communication methodincluding searching for communication channels other than a channel usedin wireless power transmission. The communication method furtherincludes measuring state information of the communication channels. Thecommunication method further includes determining a communicationchannel available for communication with a target device based on themeasured state information. The communication method further includestransmitting an access instruction to the target device using thedetermined communication channel. The communication method furtherincludes determining whether to communicate with the target device usingthe determined communication channel based on whether a response signalcorresponding to the access instruction is received.

The communication method may further include transmitting a channelseizure signal to the target device, the channel seizure signalincluding a predetermined intensity.

The measuring of the state information may include measuring intensitiesof interference signals of the respective communication channels.

The determining of the communication channel may include determining acommunication channel including an intensity of an interference signalthat is less than or equal to a predetermined value, among the measuredintensities, to be the communication channel available for communicationwith the target device.

In yet another general aspect, there is provided a communication methodin a wireless power transmission system, the communication methodincluding searching for communication channels other than a channel usedin wireless power transmission. The communication method furtherincludes measuring state information of the communication channels. Thecommunication method further includes determining a communicationchannel available for communication with a source device based on themeasured state information. The communication method further includesdetermining whether to communicate with the source device using thedetermined communication channel based on whether an access instructionis received from the source device using the determined communicationchannel.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless powertransmission system.

FIG. 2 is a diagram illustrating an example of an environment in which awireless power transmission system is exposed to different wirelesscommunication schemes.

FIG. 3 is a diagram illustrating an example of an environment in whichwireless power transmission systems perform communication using the samechannel.

FIG. 4 is a diagram illustrating an example of an operating mode of acommunication apparatus in a wireless power transmission system.

FIG. 5 is a block diagram illustrating an example of a communicationapparatus in a wireless power transmission system.

FIG. 6 is a block diagram illustrating another example of acommunication apparatus in a wireless power transmission system.

FIG. 7 is a diagram illustrating an example of communication channelsthat may be used in a wireless power transmission system.

FIG. 8 is a diagram illustrating an example of a method of a targetdevice determining a communication channel based on a continuous wave(CW) signal in a wireless power transmission system.

FIG. 9 is a graph illustrating examples of powers of CW signals receivedby a target device in a wireless power transmission system.

FIG. 10 is a graph illustrating examples of powers of communicationchannel signals received by a target device in a wireless powertransmission system.

FIG. 11 is a diagram illustrating an example of an interference signalinfluencing a source device in a wireless power transmission system.

FIG. 12 is a graph illustrating an example of a timing in which a sourcedevice determines a communication channel in a wireless powertransmission system.

FIG. 13 is a graph illustrating an example of a timing in which a targetdevice determines a communication channel in a wireless powertransmission system.

FIG. 14 is a diagram illustrating an example of wireless powertransmission systems placed in a cell unit.

FIG. 15 is a diagram illustrating an example of communication networksinfluencing communication channels of source devices in a wireless powertransmission system.

FIG. 16 is a graph illustrating an example of intensities of signalsdetected from communication channels in a wireless power transmissionsystem.

FIG. 17 is a graph illustrating an example of a relationship between apower of a signal interfering with a communication channel of a sourcedevice, and an input power in the communication channel, in a wirelesspower transmission system.

FIG. 18 is a diagram illustrating an example of a communication distancebased on an adjustment of a power output from a power source device in awireless power transmission system.

FIG. 19 is a diagram illustrating an example of a position of a targetdevice in a wireless power transmission system.

FIG. 20 is a graph illustrating an example of a power transmissionefficiency based on a position of a target device in a wireless powertransmission system.

FIG. 21 is a flowchart illustrating an example of a communication methodin a wireless power transmission system.

FIG. 22 is a flowchart illustrating another example of a communicationmethod in a wireless power transmission system.

FIG. 23 is a block diagram illustrating still another example of acommunication apparatus in a wireless power transmission system.

FIGS. 24A through 24B are diagrams illustrating examples of adistribution of a magnetic field in a feeder and a resonator of awireless power transmission system.

FIGS. 25A and 25B are diagrams illustrating an example of a wirelesspower transmitter.

FIG. 26A is a diagram illustrating an example of a distribution of amagnetic field inside a resonator produced by feeding of a feeding unit.

FIG. 26B is a diagram illustrating examples of equivalent circuits of afeeding unit and a resonator.

FIG. 27 is a diagram illustrating an example of an electric vehiclecharging system.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. Accordingly, various changes,modifications, and equivalents of the systems, apparatuses, and/ormethods described herein will be suggested to those of ordinary skill inthe art. The progression of processing steps and/or operations describedis an example; however, the sequence of steps and/or operations is notlimited to that set forth herein and may be changed as is known in theart, with the exception of steps and/or operations necessarily occurringin a certain order. Also, description of well-known functions andconstructions may be omitted for increased clarity and conciseness.

A scheme of performing communication between a source device and atarget device includes an in-band communication scheme and an out-bandcommunication scheme. The in-band communication scheme refers tocommunication performed between the source device and the target devicein the same frequency band as used for power transmission. The out-bandcommunication scheme refers to communication performed between thesource device and the target device in a separate frequency band thanused for power transmission.

FIG. 1 illustrates an example of a wireless power transmission system.The wireless power transmission system includes a source 110 and atarget 120. The source 110 refers to a device configured to supply awireless power, and may include all electronic devices enabling powersupply, for example, a pad, a terminal, a television (TV), and/or otherelectronic devices known to one of ordinary skill in the art. The target120 refers to a device configured to receive the supplied wirelesspower, and may include all electronic devices requiring power, forexample, a terminal, a TV, a vehicle, a washing machine, a radio, anelectric light, and/or other electronic devices known to one of ordinaryskill in the art.

The source 110 includes a variable switching mode power supply (SMPS)111, a power amplifier 112, a matching network 113, a controller 114, acommunication unit 115, and a power detector 116. The variable SMPS 111switches alternating current (AC) voltage in a band of tens of hertz(Hz) output from a power supply to generate direct current (DC) voltage.The variable SMPS 111 may output the DC voltage of a predeterminedlevel, or may adjust an output level of the DC voltage based on acontrol of the controller 114.

A power detector 116 detects an output current and an output voltage ofthe variable SMPS 111, and transfers, to the controller 114, informationon the detected current and the detected voltage. Additionally, thepower detector 116 may detect an input current and an input voltage ofthe power amplifier 112.

The power amplifier 112 converts the DC voltage to an AC voltage basedon a switching pulse signal in a band of a few megahertz (MHz) to tensof MHz to generate a power. For example, the power amplifier 112 mayconvert the DC voltage supplied to the power amplifier 112 to the ACvoltage based on a reference resonance frequency F_(Ref), and maygenerate a communication power used for communication, and/or a chargingpower used to charge. The communication power and the charging power maybe used in target devices.

The communication power may refer to a low power of 0.1 milliwatt (mW)to 1 mW. The charging power may refer to a high power of 1 mW to 200 Wthat is consumed in a device load of a target device. In variousexamples described herein, the term “charging” may refer to supplyingpower to a unit or element that is configured to charge power.Additionally, the term “charging” may refer to supplying power to a unitor element that is configured to consume power. The units or elementsmay include, for example, batteries, displays, sound output circuits,main processors, various sensors, and or other units or elements knownto one of ordinary skill in the art.

Also, the term “reference resonance frequency” may refer to a resonancefrequency used by the source 110. Additionally, the term “trackingfrequency” may refer to a resonance frequency adjusted by a presetscheme.

The controller 114 detects a reflected wave of the communication powerand/or the charging power, and may detect mismatching that may occurbetween a target resonator 133 and a source resonator 131 based on thedetected reflected wave. To detect the mismatching, for example, thecontroller 114 may detect an envelope of the reflected wave, a poweramount of the reflected wave, and/or other values known to one ofordinary skill in the art.

The matching network 113 compensates for impedance mismatching betweenthe source resonator 131 and the target resonator 133 to be optimalmatching, under the control of the controller 114. The matching network113 may be connected through a switch, including a combination of acapacitor and an inductor, under the control of the controller 114.

The controller 114 determines a voltage standing wave ratio (VSWR) basedon a voltage level of the reflected wave, and an output voltage of thesource resonator 131 or the power amplifier 112. For example, if theVSWR is less than a predetermined value, the controller 114 determinesthat mismatching is detected.

In this example, the controller 114 determines a power transmissionefficiency for each of N tracking frequencies, determines a trackingfrequency F_(Best) with the best power transmission efficiency among theN tracking frequencies, and adjusts the reference resonance frequencyF_(Ref) to the tracking frequency F_(Best). In various examples, the Ntracking frequencies may be set in advance.

The controller 114 adjusts a frequency of the switching pulse signal.Under the control of the controller 114, the frequency of the switchingpulse signal is determined. For example, by controlling the poweramplifier 112, the controller 114 may generate a modulation signal to betransmitted to the target 120. In other words, the communication unit115 may transmit a variety of data 140 to the target 120 using thein-band communication. The controller 114 may detect a reflected wave,and may demodulate a signal received from the target 120 through anenvelope of the detected reflected wave.

The controller 114 may generate the modulation signal for the in-bandcommunication based on various ways. For example, the controller 114 maygenerate the modulation signal by turning on and off the switching pulsesignal, by performing delta-sigma modulation, and/or other types ofmethods known to one of ordinary skill in the art. Additionally, thecontroller 114 may generate a pulse-width modulation (PWM) signal with apredetermined envelope.

The communication unit 115 may perform out-band communication employinga communication channel. The communication unit 115 may include acommunication module, such as, for example, one configured to processZigBee, Bluetooth, and/or other communication protocols known to one ofordinary skill in the art. The communication unit 115 may transmit thedata 140 to the target 120 through the out-band communication.

The source resonator 131 transfers an electromagnetic energy 130 to thetarget resonator 133. For example, the source resonator 131 may transferthe communication power and/or the charging power to the target 120based on magnetic coupling with the target resonator 133.

The target 120 includes a matching network 121, a rectification unit122, a DC-to-DC (DC/DC) converter 123, a communication unit 124, and acontroller 125, and a power detector 127. The target resonator 133receives the electromagnetic energy 130 from the source resonator 131.For example, the target resonator 133 may receive the communicationpower and/or charging power from the source 110 based on the magneticcoupling with the source resonator 131. Additionally, the targetresonator 133 may receive the data 140 from the source 110 using thein-band communication.

The matching network 121 matches an input impedance viewed from thesource 110 to an output impedance viewed from a load of the target 120.The matching network 121 may be configured with a combination of acapacitor and an inductor.

The rectification unit 122 rectifies an AC voltage to generate a DCvoltage. The AC voltage may be received from the target resonator 133.

The DC/DC converter 123 adjusts a level of the DC voltage output fromthe rectification unit 122, based on a capacity required by the load.For example, the DC/DC converter 123 may adjust the level of the DCvoltage output from the rectification unit 122 from 3 volts (V) to 10 V.

The power detector 127 detects a voltage of an input terminal 126 of theDC/DC converter 123, and a current and a voltage of an output terminalof the DC/DC converter 123. The detected voltage of the input terminal126 is used to determine a transmission efficiency of the power receivedfrom the source 110. Additionally, the detected current and the detectedvoltage of the output terminal is used by the controller 125 todetermine an amount of a power transferred to the load. The controller114 of the source 110 determines an amount of a power to be transmittedby the source 110 based on a power required by the load and the powertransferred to the load. If the power of the output terminal istransferred to the source 110 using the communication unit 124, thesource 110 may determine the amount of the power to be transmitted.

The communication unit 124 may perform in-band communication to transmitand receive data based on a resonance frequency. During the in-bandcommunication, the controller 125 detect a signal between the targetresonator 133 and the rectification unit 122, or detect an output signalof the rectification unit 122, to demodulate the detected signal. Inother words, the controller 125 may demodulate a message received usingthe in-band communication. Additionally, the controller 125 may adjustan impedance of the target resonator 133 using the matching network 121to modulate a signal to be transmitted to the source 110. For example,the controller 125 may increase the impedance of the target resonator133 so that a reflected wave may be detected by the controller 114 ofthe source 110. Depending on whether the reflected wave is detected, thecontroller 114 may detect a binary number, for example, “0” or “1”.

The communication unit 124 may transmit a response message to thecommunication unit 115 of the source 110. For example, the responsemessage may include a type of a corresponding target (e.g., the target120), information about a manufacturer of a corresponding target, amodel name of a corresponding target, a battery type of a correspondingtarget, a scheme of charging a corresponding target, an impedance valueof a load of a corresponding target, information on characteristics of atarget resonator (e.g., the target resonator 133) of a correspondingtarget, information on a frequency band used by a corresponding target,an amount of a power consumed by a corresponding target, an identifier(ID) of a corresponding target, information on version or standard of acorresponding target, and/or other information known to one of ordinaryskill in the art.

The communication unit 124 may perform out-band communication using acommunication channel. For example, the communication unit 124 mayinclude a communication module, such as, for example, one configured toprocess ZigBee, Bluetooth, and/or other communication protocols known toone of ordinary skill in the art. The communication unit 124 maytransmit and receive the data 140 to and from the source 110 using theout-band communication.

The communication unit 124 receives a wake-up request message from thesource 110, and the power detector 127 detects an amount of a powerreceived at the target resonator 133. The communication unit 124transmits, to the source 110, information on the detected amount of thepower. Information on the detected amount may include, for example, aninput voltage value and an input current value of the rectification unit122, an output voltage value and an output current value of therectification unit 122, an output voltage value and an output currentvalue of the DC/DC converter 123, and/or other values known to one ofordinary skill in the art.

The controller 114 sets a resonance bandwidth of the source resonator131. Based on the setting of the resonance bandwidth of the sourceresonator 131, a Q-factor of the source resonator 131 may be determined.

Additionally, the controller 125 sets a resonance bandwidth of thetarget resonator 133. Based on the setting of the resonance bandwidth ofthe target resonator 133, a Q-factor of the target resonator 133 may bedetermined. For example, the resonance bandwidth of the source resonator131 may be set to be wider or narrower than the resonance bandwidth ofthe target resonator 133.

The source 110 and the target 120 communicate with each other to shareinformation on the resonance bandwidth of the source resonator 131 andthe resonance bandwidth of the target resonator 133. In an example inwhich a power desired or required by the target 120 is greater than areference value, the Q-factor of the source resonator 131 may be set toa value greater than “100”. In another example in which the powerdesired or required by the target 120 is less than the reference value,the Q-factor of the source resonator 131 may be set to a value less than“100”.

In a wireless power transmission employing a resonance scheme, theresonance bandwidth is a factor. A Q-factor Qt may consider a change ina distance between the source resonator 131 and the target resonator133, a change in a resonance impedance, impedance mismatching, areflected signal, and/or other values known to one of ordinary skill inthe art. In this example, the Q-factor Qt may include aninverse-proportional relationship with the resonance bandwidth, as givenin the example of Equation 1.

$\begin{matrix}\begin{matrix}{\frac{\Delta\; f}{f_{0}} = \frac{1}{Qt}} \\{= {\Gamma_{S,D} + \frac{1}{{BW}_{S}} + \frac{1}{{BW}_{D}}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, f₀ denotes a central frequency, Δf denotes a bandwidth,Γ_(S,D) denotes a reflection loss between the source resonator 131 andthe target resonator 133, BW_(S) denotes the resonance bandwidth of thesource resonator 131, and BW_(D) denotes the resonance bandwidth of thetarget resonator 133.

An efficiency U of a wireless power transmission may be defined, asgiven in the example of Equation 2.

$\begin{matrix}{U = {\frac{\kappa}{\sqrt{\Gamma_{S}\Gamma_{D}}} = {\frac{\omega_{0}M}{\sqrt{R_{S}R_{D}}} = \frac{\sqrt{Q_{S}Q_{D}}}{Q_{K}}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Equation 2, κ denotes a coupling coefficient of energy couplingbetween the source resonator 131 and the target resonator 133, Γ_(S)denotes a reflection coefficient in the source resonator 131, Γ_(D)denotes a reflection coefficient in the target resonator 133, ω₀ denotesa resonance frequency, M denotes a mutual inductance between the sourceresonator 131 and the target resonator 133, R_(S) denotes an impedanceof the source resonator 131, R_(D) denotes an impedance of the targetresonator 133, Q_(S) denotes the Q-factor of the source resonator 131,Q_(D) denotes the Q-factor of the target resonator 133, and Q_(K)denotes a Q-factor of the energy coupling between the source resonator131 and the target resonator 133.

Referring to Equation 2, the Q-factors may include high relevance to theefficiency of the wireless power transmission. Accordingly, to increasethe efficiency of the wireless power transmission, the Q-factors may beset to high values. However, even if the Q-factors Q_(S) and Q_(D) areset to extremely high values, the efficiency of the wireless powertransmission may be decreased due to a change in the couplingcoefficient κ, the change in the distance between the source resonator131 and the target resonator 133, the change in the resonance impedance,impedance mismatching, and/or other values known to one of ordinaryskill in the art.

Additionally, to increase the efficiency of the wireless powertransmission, the resonance bandwidth of the source resonator 131, andthe resonance bandwidth of the target resonator 133, may be set to beexcessively narrow. However, in this example, impedance mismatchingand/or other issues known to one of ordinary skill in the art may occurdue to even a small external effect. Considering the impedancemismatching, Equation 1 may be represented as given in the example ofEquation 3.

$\begin{matrix}{\frac{\Delta\; f}{f_{0}} = \frac{\sqrt{VSWR} - 1}{{Qt}\sqrt{VSWR}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In an example in which an unbalanced relationship of a resonancebandwidth, or a bandwidth of an impedance matching frequency, betweenthe source resonator 131 and the target resonator 133 is maintained, adecrease in efficiency of the wireless power transmission may beprevented due to the change in the coupling coefficient κ, the change inthe distance between the source resonator 131 and the target resonator133, the change in the resonance impedance, impedance mismatching,and/or other values known to one of ordinary skill in the art. In anexample in which the unbalanced relationship of the resonance bandwidth,or the bandwidth of the impedance matching frequency, between the sourceresonator 131 and the target resonator 133 is maintained, based onEquations 1 and 3, an unbalanced relationship between the Q-factorsQ_(S) and Q_(D) may also be maintained.

FIG. 2 illustrates an example of an environment in which a wirelesspower transmission system is exposed to different wireless communicationschemes. The wireless power transmission system includes a power sourcedevice and a mobile device. The power source device and the mobiledevice perform wireless communication in the environment enabling thecommunication in an industrial, scientific, medical (ISM) band. The ISMband may refer to a band of 2.4 gigahertz (GHz). The ISM band may beused in a IEEE 802.11 wireless local area network (WLAN) (“WLAN802.11”), a IEEE 802.15 wireless personal area network (WPAN) (“WPAN802.15”), and a IEEE 802.16 wireless metropolitan area network (WMAN)(“WMAN 802.16”).

When the power source device and the mobile device communicate with eachother in the ISM band, interference of radio waves may be caused bydifferent types of wireless communication apparatuses using the WLAN802.11, the WPAN 802.15, and/or the WMAN 802.16. Accordingly, acommunication error between the power source device and the mobiledevice may occur, and a communication speed may be decreased.Furthermore, it may be difficult to control the wireless powertransmission system. In other words, if different types of wirelesselectronic devices communicate with each other, frequency interferencemay occur in the wireless power transmission system.

FIG. 3 illustrates an example of an environment in which wireless powertransmission systems perform communication using the same channel. Eachof the wireless power transmission systems includes a power sourcedevice and a mobile device. For example, when power source devicescommunicate with mobile devices using the same channel (e.g., a channelCH1), frequency interference may occur. In more detail, in a region inwhich the channel CH1 is available, the power source devices are spacedapart from each other by a predetermined distance, and share the samechannel CH1. If a power source device and/or a mobile device approacheswithin the predetermined distance, frequency interference may occurbetween the power source devices, and between the mobile device andanother power source device.

FIG. 4 illustrates an example of an operating mode of a communicationapparatus in a wireless power transmission system. The communicationapparatus includes a source device and a target device. Thecommunication apparatus operates in three modes in the wireless powertransmission system. The three modes include, for example, a powerstandby mode, a power access mode, and a power transfer mode (namely, apower charge mode).

The power standby mode refers to a mode in which a communication channelis not connected between an initialized source device and an initializedtarget device. For example, when power is supplied, the source deviceperforms basic hardware initialization, reads information from a systemconfiguration block (SCB) of the source device, and initializes systeminformation. The system information may include, for example, a serialnumber of the source device, a maximum number of target devicesaccessible to the source device, a power transmission parameter, acommunication channel parameter, and/or other information known to oneof ordinary skill in the art.

When a wake-up power is received from the source device, that is, when apower required to control a system is supplied to the target device, thetarget device performs basic hardware initialization. Subsequently, thetarget device may read a serial number of the target device, a batterytype, a power transmission parameter, a communication channel parameter,and/or other information known to one of ordinary skill in the art, froman SCB of the target device, and initializes system information. The SCBmay refer to a memory configured to support at least 8 bytes, and acapacity of the SCB may be determined based on an improvement of afunction of each of the source device and the target device, a type ofthe source device, and/or a type of the target device.

In the power standby mode, the source device determines whether a chargecommand is received at the source device. For example, if a start buttonis input, the charge command is received. In another example, if atarget device located within a predetermined distance from the sourcedevice is detected, the charge command is automatically received. Thesource device further determines states of all channels available forcommunication. For example, the source device measures a level of areceived signal strength indication (RSSI) for each channel, anddetermines whether each channel is available based on the RSSI.

In the power standby mode, the target device searches for channelsavailable for communication. For example, the target device may measurean RSSI, or a link quality indicator (LQI), of a channel. In thisexample, if the measured RSSI or the measured LQI is greater than orequal to a predetermined value, the target device determines whether apreset packet is received via the channel within a predetermined periodof time. If the measured RSSI or the measured LQI is less than thepredetermined value, the target device searches for a next channel.

A channel search mode and a channel selection mode are applied while thepower standby mode transitions to the power access mode. For example,when a target device is located within a power transmission distance ofthe source device, the source device searches for a channel enablingcommunication with the target device. In this example, the source deviceis operated in the channel search mode. In the channel selection mode,the source device selects, as a communication channel, a channelsatisfying a set condition, from among channels enabling communicationwith the target device, and shares the selected channel with the targetdevice.

If the charge command is received, the source device is operated in thepower access mode. If the source device is already accessed by a targetdevice, the source device may detect a level of a reflected wave. If thelevel of the reflected wave includes a predefined value, the sourcedevice determines that another target device exists, and is operated inthe power access mode.

If a target device is detected first, or if the charge command isreceived, the source device transmits the wake-up power via a powertransmission channel. The source device may measure an RSSI or LQI inthe communication channel enabling communication with the target. If theRSSI or LQI is measured to be greater than or equal to a referencevalue, the communication channel is determined to be a currently-usedchannel, and the source device continues to search for a next channeluntil a channel with an RSSI or LQI including a value less than thereference value is found. When the channel is found, the source devicemay fix the found channel, and transmits an access standard instruction,based on a reference in the found channel. When target devices respondto the access standard instruction, the source device assigns controlidentifiers (IDs) to the target devices in an order that the targetdevices respond to the access standard instruction.

When at least one target device is connected to the source device, thesource device transmits a wake-up power via the power transmissionchannel. The source device may transmit an access standard instructionto an additionally detected target using the communication channelalready determined. If the additionally detected target device respondsto the access standard instruction, the source device may assign controlIDs to the target devices in an order that the target devices respond tothe access standard instruction.

For example, the source device may assign control IDs “1” to “N” to thetarget devices in an ascending order. In this example, “N” indicates amaximum number of target devices accessible to the source device. When alow control ID assigned to a target device is empty due to completion ofcharging of the target device, or separation of the target device fromthe wireless power transmission system, the source device may assign thelow control ID to a new target device accessing the source device. Forexample, if three target devices are chargeable by the source device,control IDs “1” and “2” are assigned, and a target device with thecontrol ID “1” is separated from the wireless power transmission system,the source device may assign the control ID “1”, instead of a control ID“3”, to a new target device accessing the source device.

When a control ID is assigned to a target device, the source device isoperated in the power transmission mode. The source receives informationon a power required by the target device from the target device. Theinformation on the required power may be stored in an SCB of the targetdevice. The power transmission mode may be defined to be set in a periodfrom a point in time in which the source device transmits a power, to apoint in time in which a battery of the target device is completelycharged and a charge control port of the target device is blocked. Inthe power transmission mode, the source device may regularly receiveinformation on a state of the target device, a voltage and a current ofan input end of the target device, and/or a voltage and a current of anoutput end of the target device, based on rules defined in advance foreach product and for each model. The source device may perform a controloperation based on the received information.

An operation of the target device may be reset based on a resetinstruction to prevent malfunction of the target device. The malfunctionof the target may include, for example, an incorrect access to a source,overheating, abnormality in charging, and/or issues known to one ofordinary skill in the art. In more detail, the target device may includea separate port to perform an appropriate operation if the target isoverheated, and/or if the input end and the output end of the target areabnormally-operated. For example, if an abnormality occurs, the targetdevice transmits information on the abnormality, while requesting astate of the source device. The target device may verify a temperature,a charging voltage, and/or a supplied power, regardless of the sourcedevice, and may terminate charging through a separate processing path.

In another example, if no response is received from the target device,or if a checksum error in a signal transmitted by the source occurs atleast a predetermined number of times, the source device changes acurrently used communication channel. In this example, the source deviceis operated in a channel change mode.

FIG. 5 illustrates an example of a communication apparatus 500 in awireless power transmission system. The communication apparatus 500includes a channel search unit 510, a channel determining unit 520, acontroller 530, and a communication unit 540. The communicationapparatus 500 of FIG. 5 may correspond to a source device in thewireless power transmission system.

The channel search unit 510 searches for communication channels. Thecommunication channels may be different from a channel used in wirelesspower transmission. The source device may transmit a power using awireless power transmission channel, and may transmit and receive datausing a communication channel. The communication channels may bechannels in an ISM band.

The channel search unit 510 selects an n-th channel, as a first targetto be searched for, from among searchable channels. For example,channels may be searched for in a descending order, in an ascendingorder, or in a random order.

The channel search unit 510 may search for communication channels basedon a search table. The search table may be set differently based on atype of the source device or a unique ID assigned to the source device.The channel search unit 510 may search for communication channels indifferent orders for each type of the source device, as illustrated inthe example of Table 1. In an example in which the source devicecorresponds to a type 1, the channel search unit 510 sequentiallysearches for 16 channels. In another example in which the source devicecorresponds to a type 5, the channel search unit 510 sequentiallysearches for the 16 channels from a channel 2.

TABLE 1 Search table (16 channels, 1~16) Type of source or unique IDType1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 assigned to source Type2 45 6 7 8 9 10 11 12 13 14 15 16 1 2 3 Type3 10 11 12 13 14 15 16 1 2 3 45 6 7 8 9 Type4 7 8 9 10 11 12 13 14 15 16 1 2 3 4 5 6 Type5 2 3 4 5 6 78 9 10 11 12 13 14 15 16 1 Type6 14 15 16 1 2 3 4 5 6 7 8 9 10 11 12 13Type7 9 10 11 12 13 14 15 16 1 2 3 4 5 6 7 8 Type8 16 1 2 3 4 5 6 7 8 910 11 12 13 14 15 Type9 12 13 14 15 16 1 2 3 4 5 6 7 8 9 10 11 Type10 67 8 9 10 11 12 13 14 15 16 1 2 3 4 5 Type11 5 6 7 8 9 10 11 12 13 14 1516 1 2 3 4 Type12 11 12 13 14 15 16 1 2 3 4 5 6 7 8 9 10 Type13 8 9 1011 12 13 14 15 16 1 2 3 4 5 6 7 Type14 13 14 15 16 1 2 3 4 5 6 7 8 9 1011 12 Type15 15 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Type16 3 4 5 6 7 8 910 11 12 13 14 15 16 1 2

The channel search unit 510 measures state information of one or morecommunication channels. The state information may include information onwhether the communication channels are used by other source devicesand/or different types of communication apparatuses.

For example, the channel search unit 510 includes a channel measuringunit 511. The channel measuring unit 511 measures intensities ofinterference signals of the respective communication channels. Forexample, the channel measuring unit 511 may measure an RSSI or LQI of acommunication channel.

The channel determining unit 520 determines a communication channelavailable for communication with a target device based on the stateinformation of the communication channels. The target device may bedetected in a wireless power transmission region of the source device.For example, the channel determining unit 520 determines a communicationchannel with little interference by neighboring devices to be thecommunication channel available for communication with the targetdevice. The channel determining unit 520 may determine a communicationchannel including an intensity of an interference signal that is lessthan or equal to a predetermined reference value, among the measuredintensities, to be the communication channel available for communicationwith the target device. For example, the channel determining unit 520may determine a communication channel with a minimum RSSI to be thecommunication channel available for communication with the targetdevice.

The communication unit 540 transmits a channel seizure signal and anaccess standard instruction to the target device based on acommunication frequency of the determined communication channel. Thechannel seizure signal may include a predetermined intensity. Thechannel seizure signal may be a continuous wave (CW) signal includingthe predetermined intensity and a power greater than a communicationsignal of a direct-sequence spread spectrum (DSSS). The channel seizuresignal may be modulated based on a predetermined modulation scheme.

The access standard instruction may include information used forcompatibility between the source device and the target device. Theaccess standard instruction may include a call argument and a callparameter used to identify target devices. For example, if the sameidentifying parameter as a call parameter is included in the targetdevice, the target device transmits, to the source device, a responsesignal.

The controller 530 determines whether to communicate with the targetdevice using the determined communication channel based on whether aresponse signal corresponding to the access standard instruction isreceived. For example, if the response signal is received from thetarget device, the controller 530 determines to communicate with thetarget device using the determined communication channel. In response tothe response signal, the controller 530 assigns a control ID to thetarget device.

The communication unit 540 receives, from the target device, a responsesignal indicating that the control ID is assigned to the target device.If the control ID is assigned to the target device, the communicationunit 540 transmits a signal requesting information on a power requiredby the target device, using the communication frequency of thedetermined communication channel. The communication unit 540 receivesthe information on the power required by the target device from thetarget device.

The controller 530 determines an amount of a wireless power to betransmitted by the source device based on the information on the powerrequired by the target device. Additionally, the controller 530 controlsan amount of a power in the source device so that the source devicetransmits a power corresponding to the determined amount of the wirelesspower.

The controller 530 controls the operation of the channel search unit510, regardless of whether the target device is waked up. For example,before the target device is detected, the controller 530 controls thechannel search unit 510 to search for communication channels availablefor communication in the source device.

In an example in which the source device is not accessed by a targetdevice, the controller 530 controls the operation of the channel searchunit 510 based on a channel search start command. For example, if a userpushes a start button attached to the source device, the channel searchstart command is input.

In another example in which the source device is accessed by a targetdevice, the controller 530 controls the operation of the channel searchunit 510 based on an amount of a change in a current output from thesource device. This is because the current output from the source devicemay be changed if another target device is added, or if the targetdevice disappears.

If the source device is operated in the power access mode, thecontroller 530 determines whether the source device is accessed by thetarget device based on information on a power of a communication outputof the source device, and information on a power of the communicationoutput received by the target device. The power of the communicationoutput of the source device refers to a power used to transmit data viaa communication channel. If a difference between the power of thecommunication output of the source device and the power of thecommunication output received by the target, is less than apredetermined reference, the controller 530 permits the target device toaccess the source device. As a distance between the source device andthe target device is reduced, a low amount of the power of thecommunication output transmitted from the source device to the targetdevice may be lost. The source device may permit an access by a targetdevice located near the source device first.

The controller 530 may determine a difference between a wireless powertransmitted by the source device and a power transferred to a load ofthe target device, and may determine whether the target deviceincorrectly accesses the source device based on the calculateddifference. If the calculated difference is greater than a predeterminedreference, the controller 530 determines that the target deviceincorrectly accesses the source device. In other words, whether thetarget device incorrectly accesses the source device may be determinedbased on a wireless power transmission efficiency.

Additionally, the controller 530 may determine a difference between atime in which an amount of the wireless power transmitted by the sourcedevice is changed to a predetermined value, and a time in which anamount of the power transferred to the load of the target device ischanged, and may determine whether the target device incorrectlyaccesses the source based on the calculated difference. If thecalculated difference is greater than a predetermined reference, thecontroller 530 determines that the target device incorrectly accessesthe source device.

If an interference signal including an intensity level greater than orequal to a channel selection reference level (i.e., of intensity), ismeasured in each of the communication channels as a result of measuringthe state information of the communication channels, the channeldetermining unit 520 determines a communication channel with aninterference signal including a lowest intensity level, among themeasured intensities, to be the communication channel available forcommunication with the target device. Otherwise, the channel determiningunit 520 determines a communication channel with an interference signalof a level less than or equal to the channel selection reference level,among the measured intensities to be the communication channel availablefor communication with the target device.

The controller 530 determines a power level of the communication outputof the source device based on a table to which an intensity level of aninterference signal in the determined communication channel, and a powerlevel of an output signal required to transmit data within apredetermined error range, are mapped. As the intensity level of theinterference signal increases, the power level of the communicationoutput of the source device may need to increase, to transmit datawithin the predetermined error range.

If a value of an error in a communication channel between the sourcedevice and the target device becomes greater than a predeterminedreference value, or if an intensity of an interference signal detectedfrom the determined communication channel is greater than apredetermined value, the controller 530 determines to change thedetermined communication channel to another communication channel. Thecontroller 530 determines a new communication channel using the channeldetermining unit 520. The controller 530 transmits, to the targetdevice, a channel change request instruction including information onthe new communication channel.

The controller 530 controls an overall operation of the communicationapparatus 500, and performs functions of the channel search unit 510,the channel determining unit 520, and the communication unit 540. Toindividually describe functions of the channel search unit 510, thechannel determining unit 520, the controller 530, and the communicationunit 540, the channel search unit 510, the channel determining unit 520,the controller 530, and the communication unit 540 are separatelyillustrated in FIG. 5. However, if the communication apparatus 500 ofFIG. 5 is implemented, the controller 530 may be configured to performall of the functions, or only a portion of the functions.

FIG. 6 illustrates another example of a communication apparatus 600 in awireless power transmission system. The communication apparatus 600includes a communication unit 610, a controller 620, a channel searchunit 630, and a channel determining unit 640. The communicationapparatus 600 of FIG. 6 may correspond to a target device in thewireless power transmission system.

The channel search unit 630 searches for communication channels. Thecommunication channels may be different from a channel used in wirelesspower transmission. The target device may receive a power using awireless power transmission channel, and may transmit and receive datausing a communication channel. The communication channels may bechannels in an ISM band.

The channel search unit 630 selects an n-th channel, as a first targetto be searched for, from among searchable channels. For example,channels may be searched for in a descending order, in an ascendingorder, or in a random order.

The channel search unit 630 may search for communication channels basedon a search table. The search table may be set differently based on atype of a target device or a unique ID assigned to the target device.The channel search unit 630 may search for communication channels indifferent orders for each type of the target device, as illustrated inthe example of Table 2. In an example in which the target devicecorresponds to a type 1, the channel search unit 630 may sequentiallysearch for 16 channels from a channel 7. In another example in which thetarget device corresponds to a type 5, the channel search unit 630 maysequentially search for the 16 channels from a channel 9.

TABLE 2 Search table (16 channels, 1~16) Type of target, or unique IDType1 7 8 9 10 11 12 13 14 15 16 1 2 3 4 5 6 assigned to target Type2 23 4 5 6 7 8 9 10 11 12 13 14 15 16 1 Type3 10 11 12 13 14 15 16 1 2 3 45 6 7 8 9 Type4 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 Type5 9 10 11 1213 14 15 16 1 2 3 4 5 6 7 8 Type6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Type7 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Type8 12 13 14 15 16 1 2 34 5 6 7 8 9 10 11 Type9 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4 5 Type10 1112 13 14 15 16 1 2 3 4 5 6 7 8 9 10 Type11 4 5 6 7 8 9 10 11 12 13 14 1516 1 2 3 Type12 15 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Type13 5 6 7 8 910 11 12 13 14 15 16 1 2 3 4 Type14 8 9 10 11 12 13 14 15 16 1 2 3 4 5 67 Type15 13 14 15 16 1 2 3 4 5 6 7 8 9 10 11 12 Type16 14 15 16 1 2 3 45 6 7 8 9 10 11 12 13

The channel search unit 630 measures state information of one or morecommunication channels. The state information may include information ona channel seizure signal transmitted by the source device. The channelseizure signal may include a predetermined intensity. For example, thechannel seizure signal may be a CW signal including a predeterminedintensity and a power greater than a communication signal of a DSSS. Thechannel seizure signal may be modulated using a predetermined modulationscheme. The channel search unit 630 may search for a channel thatenables receiving of a CW signal. The channel search unit 630 maymeasure an RSSI of a communication channel, and may determine whetherthe channel seizure signal is received based on the RSSI.

The channel determining unit 640 determines a communication channelavailable for communication with the source device based on the stateinformation of the communication channels. The channel determining unit640 may determine a channel in which a channel seizure signal includingan intensity exceeding a predetermined reference value is measured, tobe the communication channel available for communication with the sourcedevice. The channel seizure signal may be received from the sourcedevice, and may include a predetermined intensity. An intensity of thechannel seizure signal received by the target device may be determinedbased on a distance between the source device and the target device. Thesource device and the target device may agree to communicate with eachother within a predetermined distance only.

The controller 620 determines whether to communicate with the sourcedevice based on whether an access standard instruction is received fromthe source device within a reference time using a communicationfrequency of the determined communication channel. The reference timemay be set in advance based on a state of a battery of the targetdevice, and/or other factors known to one of ordinary skill in the art.

For example, if data of communication networks other than the accessstandard instruction is received, the controller 620 determines that thereceived data is different from the access standard instruction, due todifferent packet structures. If the access standard instruction is notreceived within the reference time, the controller 620 controls thechannel search unit 630 to search for another communication channel.

The access standard instruction may include information used forcompatibility between a source device and a target device. The accessstandard instruction may include a call argument and a call parameterused to identify target devices. For example, if the same identifyingparameter as a call parameter is included in the target device, thetarget device transmits a response signal.

The communication unit 610 receives an access standard instruction froma source device. For example, if the access standard instruction isreceived within a reference time, the communication unit 610 transmits aresponse signal corresponding to the access standard instruction.

The communication unit 610 receives a control ID assigned to the targetdevice from the source device. If the response signal corresponding tothe access standard instruction is received, the source device assignsthe control ID to the target device.

For example, if channel seizure signals are received from sourcedevices, the controller 620 determines a source device that uses acommunication channel with a channel seizure signal including a largestintensity, from among the source devices, to be a source device that thetarget device desires to access. In this example, the channeldetermining unit 640 determines the communication channel with thechannel seizure signal including the largest intensity to be thecommunication channel available for communication with the sourcedevice.

The controller 620 determines a power required by the target based on apower measured at an input end of a DC/DC converter included in thetarget device, a power measured at an output end of the DC/DC converter,and a power transferred to a load of the target device. Thecommunication unit 610 transmits, to the source device, information onthe power measured at the input end of the DC/DC converter, andinformation on the power measured at the output end of the DC/DCconverter. The source device may adjust a power to be transmitted to thetarget device so that the power measured at the input end of the DC/DCconverter may include a similar value to the power measured at theoutput end of the DC/DC converter. The source device receivesinformation on the power required by the target device, in real time orperiodically, and accordingly, may efficiently transmit the powerrequired by the target device to the target device.

The communication unit 610 receives a channel change request instructionfrom the source device. The controller 620 changes a channel used toaccess the source device based on communication channel informationincluded in the channel change request instruction. The communicationunit 610 may not transmit an acknowledgement (ACK) signal.

The controller 620 controls an overall operation of the communicationapparatus 600, and performs functions of the communication unit 610, thechannel search unit 630, and the channel determining unit 640. Toindividually describe functions of the communication unit 610, thecontroller 620, the channel search unit 630, and the channel determiningunit 640, the communication unit 610, the controller 620, the channelsearch unit 630, and the channel determining unit 640 are separatelyillustrated in FIG. 6. However, if the communication apparatus 600 ofFIG. 6 is implemented, the controller 620 may be configured to performall of the functions, or only a portion of the functions.

FIG. 7 illustrates an example of communication channels that may be usedin a wireless power transmission system. In the wireless powertransmission system, a communication apparatus may use channels in anISM band. In more detail, the communication apparatus may use, as acommunication channel, a single channel among 16 channels CH1 throughCH16 with a channel spacing of 5 megahertz (MHz) in a range of 2405 MHzto 2480 MHz.

FIG. 8 illustrates an example of a method a target device determining acommunication channel based on a CW signal in a wireless powertransmission system. The wireless power transmission system includes apower source device and a mobile device. The mobile device correspondsto a target device. The power source device transmits a power, and themobile device receives the power. To efficiently transmit the power tothe mobile device, the power source device may need to be aware ofinformation on a state of the mobile device. In other words, the powersource device and the mobile device may need to communicate with eachother, to exchange information on a state of the power source device andthe information on the state of the mobile device with each other.

The power source device may search for communication channels in an ISMband. Additionally, the power source device may measure an RSSI for eachof the communication channels, and may determine a communication channelin which an RSSI is less than a reference value, to be a communicationchannel available for communication with the mobile device.

To communicate with the mobile device using the determined communicationchannel, the power source device raises a power in the determinedcommunication channel, and transmits a channel seizure signal in thedetermined communication channel. While searching for communicationchannels in the ISM band, the mobile device may determine thecommunication channel receiving the channel seizure signal, to be acommunication channel available for communication with the power sourcedevice. The channel seizure signal may be, for example, a CW signal, amodulated signal, or a predetermined signal. Such a method ofdetermining a communication channel by detecting a channel seizuresignal between the power source device and the mobile device may bereferred to the term “multi-channel carrier sense-seizure of channel(MCCS-CS)”.

For example, if channel seizure signals are received, the mobile devicemay determine a communication channel with a channel seizure signalincluding a largest intensity among the received channel seizuresignals, to be a communication channel available for communication withthe power source device. The mobile device may access the power sourcedevice using the determined communication channel.

Referring to FIG. 8, a first mobile device (i.e., a mobile device 1)receives CW signals CW1 and CW2 from a first power source device (i.e.,a power source device 1) and a second power source device (i.e., a powersource device 2), respectively. CW signals transmitted by the same typeof power source devices may include the same intensity. Accordingly, anintensity of a CW signal received by a mobile device may be determinedbased on a distance between the mobile device and a power source device.Since a distance between the first mobile device and the first powersource device is shorter than a distance between the first mobile deviceand the second power source device, an intensity of the CW signal CW1 isgreater than an intensity of the CW signal CW2. The first mobile devicecommunicates with the first power source device using a communicationchannel receiving the CW signal CW1, and accesses the first power sourcedevice. Subsequently, the first mobile device receives a power from thefirst power source device.

A CW signal may be used to identify the same type of power sourcedevices, and to identify different types of communication devices.Additionally, the CW signal may be used by a target device to identifycommunication channels. The CW signal may be a carrier frequency signalthat is not modulated using an offset-quadrature phase-shift keying(O-QPSK), and an occurrence of the CW signal may be controlled by afrequency synthesizer.

To communicate with a target device based on a channel assignmentpolicy, a source device may select a channel. The target device may be,for example, a charging terminal. In wireless power transmission, 16channels may be physically supported. Each of the 16 channels may begenerated with different energy intensities. When wireless powertransmission is started, the source device may perform energy detectionof interference signals caused by different types of devices, and on CWsignals occurring from source devices of the same type as the sourcedevice. The source device may perform energy detection if all channelsbased on a frequency channel policy. The energy detection may be used bythe source device to search for a channel to communicate with multipletarget devices, in a charging environment of the multiple targetdevices.

The CW signal may be used to detect a channel. In addition, to detect achannel, a modulated signal or a predetermined signal may be used. Totransfer information on the detected channel, the source device mayincrease an intensity of the CW signal in the detected channel, and mayenable the target device to easily detect the channel. Accordingly, thetarget device may easily identify a channel available for communicationbased on a CW signal including a large intensity.

For example, if an unused channel is found as a result of searching, asource device may set transmission of a CW signal for stablecommunication between the source device and a target device. In thisexample, if the transmission of the CW signal is set by the sourcedevice, the target device may stably detect an RSSI or LQI, which mayfacilitate detection of a channel.

In a multi-charging environment, if a source device detects a channel, avalue of an RSSI based on an intensity of a CW signal may be used todetermine which type of device interferes with the source device. Inother words, the CW signal may be used to determine whether a devicethat is of the same type as the source device and that transmits awireless power, or a device that is of a different type than the sourcedevice and that does not transmit wireless power, interferes with thesource device. In an example in which a device of the same type as thesource device interferes with the source device, a difference in RSSIlevel of a CW signal may occur. In another example in which a device ofa different type than the source device interferes with the sourcedevice, a difference between a DSSS and a level of the CW signal mayoccur.

If the same channel is shared with a device of the same type as thesource device, the source device may use a CW signal to determinewhether the channel is available. If a charging source device is addedby using the CW signal as a channel seizure signal, a distance betweenthe source device and the charging source device may be determined.

The target device may use a CW signal to identify an interference with acommunication channel. The target device may distinguish a typicalinterference signal from a CW signal, and may quickly detect acommunication channel. To determine a communication channel, the targetdevice may determine whether a CW signal is received, and verify stateinformation of a source device. The target device may attempt to accessthe source device, only if an access standard instruction is received.

FIG. 9 illustrates examples of powers of CW signals received by a targetdevice in a wireless power transmission system. In a channel with acentral frequency of 2405 MHz, a communication power of an interferencesignal received from neighboring electronic devices corresponds to asignal of a DSSS. The signal of the DSSS includes a bandwidth of 5 MHz.The signal of the DSSS is lesser in intensity than, and is wider inbandwidth than, CW signals received from the same type of sourcedevices.

The target device determines a channel, and a source device tocommunicate with the target device, based on an intensity of a channelseizure signal received via the channel. Referring to FIG. 9, the targetdevice receives CW signals CW1 and CW2 (i.e., channel seizure signals)using the same channel. Since a power of the CW signal CW1 is greaterthan a power of the CW signal CW2, the target device determines toaccess a source device transmitting the CW signal CW1, and determinesthe channel with the central frequency of 2405 MHz to be a communicationchannel.

FIG. 10 illustrates examples of powers of communication channel signalsreceived by a target device in a wireless power transmission system.Source devices transmit channel seizure signals using the samecommunication scheme as neighboring electronic devices (i.e., the sameout-band channel and same bandwidth), unlike in FIG. 9. However, thesource devices increases a power of the channel seizure signals,compared to a communication power of an interference signal receivedfrom the neighboring electronic devices, and transmits the channelseizure signals with the increased power.

For example, the target device receives a first channel seizure signaland a second channel seizure signal of a channel detection power 1 and achannel detection power 2, respectively. The target device compares thechannel detection power 1 with the channel detection power 2. Since thechannel detection power 1 is greater than the channel detection power 2,the target device accesses a source device transmitting the firstchannel seizure signal. Additionally, to communicate with the sourcedevice transmitting the first channel seizure signal, the target devicedetermines the out-band channel to be a communication channel.

FIG. 11 illustrates an example of an interference signal influencing asource device in a wireless power transmission system. In more detail, asource device S1 1110 searches for a communication channel. If thecommunication channel is found, the source device S1 1110 receives aninterference signal from a WLAN 1130. The WLAN 1130 may be of adifferent type from the source device S1 1110, and may not transmitwireless power. Additionally, the source device S1 1110 receives a CWsignal from a source device S2 1120. The source device S2 1120 is of thesame type as the source device S1 1110, and transmits a wireless power.The source device S1 1110 measures an intensity (e.g., an RSSI) of theinterference signal and an intensity (e.g., an RSSI) of the CW signal,for each communication channel. If one of the intensities is less thanor equal to a predetermined value, the source device S1 1110 determinesa corresponding channel to be a communication channel.

FIG. 12 illustrates an example of a timing in which a source devicedetermines a communication channel in a wireless power transmissionsystem. The source device searches for communication channels, anddetects an RSSI for each of the communication channels.

In a time T_(S) _(—) _(PLL) 1201, the source device adjusts a channelfrequency to be a frequency of a channel to be searched for. In a timeT_(DLY) 1203, the source device stabilizes the adjusted channelfrequency. In a time T_(CHK) 1205, the source device detects an RSSI ofthe channel. If a level of the RSSI of the channel is greater than areference value, the source device determines that the channel is beingused, and searches for a next channel, as shown herein.

In a time T_(S) _(—) _(PLL) 1211, the source device adjusts a channelfrequency to be a frequency of the next channel. In a time T_(DLY) 1213,the source device stabilizes the adjusted channel frequency. In a timeT_(CHK) 1215, the source device detects an RSSI of the next channel. Ifa level of the RSSI of the next channel is less than or equal to thereference value, the source device determines the next channel to be acommunication channel for communication with a corresponding targetdevice, as shown herein. The time T_(CHK) 1215 may be set differentlybased on a type of the source device, or a type of a target deviceaccessing the source device.

In a time T_(CON) 1221, the source device transmits an access standardinstruction. In a time T_(D) 1223, the source device waits for receptionof a response signal corresponding to the access standard instruction.The access standard instruction may include information used to connectthe source device and the target device. Additionally, the accessstandard instruction may include an instruction to request stateinformation of the target device. In a time T_(CON) 1231, the sourcedevice transmits a new access standard instruction. In a time T_(D)1233, the source device waits for reception of a response signalcorresponding to the new access standard instruction.

FIG. 13 illustrates an example of a timing in which a target devicedetermines a communication channel in a wireless power transmissionsystem. The target device searches for communication channels, anddetects an RSSI for each of the communication channels.

In a time T_(S) _(—) _(PLL′) 1301, the target device adjusts a channelfrequency to be a frequency of a channel to be searched for. In a timeT_(DLY′) 1303, the target device stabilizes the adjusted channelfrequency. In a time T_(CHK′) 1305, the target device detects an RSSI ofthe channel to determine whether a channel seizure signal is receivedvia the channel. If the level of the RSSI is less than a referencevalue, the target device determines that the source device does nottransmit a channel seizure signal, and searches for a next channel, asshown herein.

In a time T_(S) _(—) _(PLL′) 1311, the target device adjusts a channelfrequency to be a frequency of the next channel. In a time T_(DLY′)1313, the target device stabilizes the adjusted channel frequency. In atime T_(CHK′) 1315, the target device detects an RSSI of the nextchannel. If a level of the RSSI of the next channel is greater than orequal to the reference value, the target device determines the nextchannel to be a communication channel for communication with acorresponding source device, as shown herein. The time T_(CHK′) 1315 maybe set differently based on a type of the target device, or a type ofthe source device accessed by the target device.

In a time T_(CHK) _(—) _(C) 1321, the target device waits for receptionof an access standard instruction from the source device. If the accessstandard instruction is not received in the time T_(CHK) _(—) _(C) 1321,as shown herein, in a time T_(S) _(—) _(PLL′) 1331, the target deviceagain adjusts a channel frequency to be a frequency of a next channel.In a time T_(DLY′) 1333, the target device stabilizes the adjustedchannel frequency. In a time T_(CHK′) 1335, the target device detects anRSSI of the next channel. If a level of the RSSI of the next channel isgreater than or equal to the reference value, the target devicedetermines the next channel to be a communication channel forcommunication with a corresponding new source device, as shown herein.

In a time T_(CHK) _(—) _(C) 1341, the target device waits for receptionof a new access standard instruction from the new source device. If thenew access standard instruction is received in the time T_(CHK) _(—)_(C) 1341, as shown herein, in a time 1343, the target device transmitsan ACK signal to the new source device.

FIG. 14 illustrates an example of wireless power transmission systemsplaced in a cell unit. Each of the wireless power transmission systemsincludes a power source device and at least one mobile device. Themobile device corresponds to a target device.

The wireless power transmission systems are managed in the cell unit. Acell includes regions in which channels may be used. A relationshipbetween cells of FIG. 14 and channels may be defined, as illustrated inthe example of Table 3.

TABLE 3 Available channel Interference channel Shared channel Cell 1Ch1, Ch2, Ch3, Ch4, Ch8, Ch9, Ch10, Ch11, Cell 2 - Ch1, Ch4 Ch5, Ch6,Ch7 Ch12, Ch13, Ch14, Cell 3 - Ch4, Ch7 Ch15, Ch16 Cell 2 Ch1, Ch4, Ch8,Ch9, Ch2, Ch3, Ch5, Ch6, Cell 1 - Ch1, Ch4 Ch10, Ch11, Ch12 Ch7, Ch13,Ch14, Cell 3 - Ch4, Ch8 Ch15, Ch16 Cell 3 Ch4, Ch7, Ch8, Ch13, Ch1, Ch2,Ch3, Ch5, Cell 1 - Ch4, Ch7 Ch14, Ch15, Ch16 Ch6, Ch9, Ch10, Ch11, Cell2 - Ch4, Ch8 Ch12

In Table 3, an available channel refers to a channel that may be used toperform communication in a wireless power transmission system.Additionally, an interference channel refers to a channel that may notbe used due to interference of signals generated from networks, such as,for example a WLAN 802.11, a WPAN 802.15, and a WMAN 802.16. A sharedchannel refers to a channel that may be shared since a distance betweenregions in different cells is greater than a predetermined reference. Inthe shared channel, an interference signal may include a low level, andinterference may be less likely to occur between different cells.Whether a channel in a cell is available in another cell may bedetermined based on whether a value of an LQI or a value of an RSSI isless than or equal to a reference value. For example, referring to FIG.14, wireless power transmission systems in the region 1410 and region1420, respectively, share a channel CH1, wireless power transmissionsystems in the region 1430 and region 1440, respectively, share achannel CH4, and wireless power transmission systems in the region 1450and region 1460, respectively, share a channel CH7.

Referring to Table 3 and FIG. 14, a cell 1 and a cell 2 share channelsCH1 and CH4, and the cell 1 and a cell 3 share channels CH4 and CH7.Additionally, the cell 2 and the cell 3 share channels CH4 and CH8.

For example, when source devices of the same type are used in a shortdistance, a target device required to be charged may access a sourcedevice other than a desired source device that the target device needsto access. To prevent the target device from accessing a source deviceother than the desired source device, a basic processing scheme, aprocessing scheme in an access mode, a processing scheme in a chargingmode, and a processing scheme of preventing an error in access, may beprovided.

In a basic processing scheme, to prevent the target device fromincorrectly accessing a source device other than the desired sourcedevice, among the source devices of the same type, the desired sourcedevice may be operated in a master mode. The desired source device inthe master mode may process an access by the target device, regardlessof whether the target device is waked up.

In an example in which no target device accesses a source device, thesource device may start processing an access of a target device usingonly a start button. Only the source device, of which the start buttonis pushed, among the source devices, may process the access, andaccordingly, a possibility for the target device to incorrectly accessanother source device may be reduced. Additionally, it is possible toreduce waste of unnecessary power in a standby mode. In another examplein which a target device accesses a source device, if a supplied currentis changed in the source device, the source device may process theaccess by the target device.

In a processing scheme in an access mode, if an access standardinstruction is transmitted from a source device to a target device, orif a source device transmits an access standard instruction using acommunication channel, information on used power may be included in theaccess standard instruction, and may be transferred to the targetdevice. The target device may transfer the received information, andinformation on a power to be transmitted, to the source device, andaccordingly, it is possible to prevent the target device fromincorrectly accessing the source device.

In more detail, the source device may transmit, to the target device, anaccess standard instruction including a communication output of acontrol channel, namely, a communication channel. The target device maytransmit, to the source device, a response signal including a value ofan LQI or a value of an RSSI of a packet received from the sourcedevice, and including a communication output of a current controlchannel.

Based on the information acquired by the above methods, the sourcedevice may verify the LQI or RSSI of the packet received by the targetdevice, the communication output transmitted by the target device, andan LQI or RSSI of a packet transmitted by the target device, compared tothe communication output of the source device. The source device maycalculate a distance between the source device and the target devicebased on the verified information. Exchanging of the information on thecommunication output of the source device and information on thecommunication output of the target device with each other, may berequired to prepare for adjustment of an output of a control channelbased on a usage environment, and of an applied product, and may berequired to prepare for a case in which the source device and the targetdevice independently determine an incorrect access.

In a processing scheme in a charging mode, if target devices are beingcharged by source devices A and B in a short distance, and if a newtarget device approaches the source devices A and B, which one of thesource devices A and B to be accessed by the new target device, may needto be determined. In this example, a target device may incorrectlyaccess a source device since at least two source devices of the sametype are located close enough to the target device. The source device Amay be incorrectly accessed by the target device, and the source deviceB may need to be accessed by the target device. Additionally, a targetdevice C may be required to be charged.

The source device A may raise a power, and transmit a higher power tothe target device C; however, a relatively low power may be transferredto the target device C, compared to a normal access. The source device Amay regularly receive, from the target device C, a power of an input endof the target device C, a power of an output end of the target device C,and state information of the target device C. The source device A maydetermine that the target device C incorrectly accesses the sourcedevice A based on the received power of the input end of the targetdevice C, the received power of the output end of the target device C,and the received state information of the target device C.

The source device A may transmit a target reset instruction to thetarget device C, and may cancel registration of a control ID assigned tothe target device C. Additionally, the source device A may enable alight-emitting diode (LED) indicator indicating a charging mode toflicker for five seconds.

In response to the target reset instruction, the target device C may beinitialized, and may be automatically disconnected from the sourcedevice A. Subsequently, the target device C may determine whether toaccess the source device B based on a state of the source device B.

If no target device accesses the source device B, and if the targetdevice C is initialized before a maximum access time elapses, the targetdevice C may directly access the source device B. For example, themaximum access time may be from about 5 seconds to 10 seconds. Themaximum access time may be adjusted based on user conveniences. If thetarget device C is initialized after the maximum access time elapses, auser may re-push a charging start button of a source device.

If a target device accesses the source device B, a current supplied inthe source device B may be changed due to an access by the target deviceC. Accordingly, the source device B may detect a change in the suppliedcurrent, and may process the access.

In a processing scheme of preventing error in access, a source devicemay adjust an output level of a CW signal to a target device, and mayreduce a communication distance. The source device may detect the outputlevel of the CW signal, and may verify the communication distance, basedon an RSSI table written for each distance from the source device.

A target device may re-adjust a transmission mode, namely, a time inwhich a response signal or other signals are transmitted. The targetdevice may further reduce a time required to connect a channel and toperform communication between a source device and the target device.

A source device may display an access attempt event (i.e., a flag), andmay use the access attempt event to indicate a source device that isattempting to access. The source device may insert, in a transmittedpacket, state indication information indicating that an attempt toaccess is being performed.

If it is difficult to perform communication due to an interferenceoccurring in a communication channel between a source device and atarget device, the source device may transmit a channel change requestinstruction, and may change the communication channel. Whether aninterference of a channel occurs, and a level of an interference, may bedetermined based on a packet error and a communication error packetcounter.

If a source device performs communication in a dense space, acommunication reception sensitivity may be reduced. The source devicemay increase a communication output level in only a communicationinterval.

A source device may cancel a general instruction if an access standardinstruction is transmitted to a target device. A source device mayprevent a target device from being operated in an access mode, in amaximum access state.

FIG. 15 illustrates an example of communication networks influencingcommunication channels of source devices in a wireless powertransmission system. When source devices S1 and S2 search forcommunication channels, a WPAN 802.15 may interfere with the sourcedevices S1 and S2 in a channel CH1, a WMAN 802.16 may interfere with thesource devices S1 and S2 in a channel CH2, and a WLAN 802.11 mayinterfere with the source devices S1 and S2 in a channel CH3. In anexample in which three communication channels, namely, the channels CH1to CH3, are available to the source devices S1 and S2, a reference todetermine a communication channel may be required. The source devices S1and S2 may wait until the interference is reduced, and may thendetermine a communication channel. Other channel determinationreferences will be described with reference to FIG. 16.

FIG. 16 illustrates an example of intensities of signals detected fromcommunication channels in a wireless power transmission system.Interference signals include intensity levels 1620, 1630, and 1640,respectively, which are higher than a channel selection reference level1610. The levels 1620, 1630, and 1640 are detected from channels CH1,CH2, and CH3, respectively. A WPAN 802.15, a WMAN 802.16, and a WLAN802.11 may interfere with the channels CH1, CH2, and CH3. A first sourcedevice may select, as a communication channel, the channel CH1 with theinterference signal including a lowest intensity level among thechannels CH1, CH2, and CH3, and may transmit a CW signal CW1 1650 to atarget device. Subsequently, a second source device may select, as acommunication channel, the channel CH2 with the interference signalincluding a lower intensity level among the channels CH2 and CH3, andmay transmit a CW signal CW2 1660 to the target device.

FIG. 17 illustrates an example of a relationship between a power of asignal interfering with a communication channel of a source device, andan input power in the communication channel, in a wireless powertransmission system. For example, if the source device selects acommunication channel from among communication channels in which levelsof interference signals are higher than a channel selection referencelevel, an input power of the selected communication channel may need tobe increased based on a power level of an interference signal of theselected communication channel, to reduce a data transmission errorrate. Referring to FIG. 17, when an output of an interference signal(namely, an interferer power) is increased, a power input into acommunication channel may also need to be increased, to reduce a datatransmission error rate to less than 1%.

FIG. 18 illustrates an example of a communication distance based on anadjustment of a power output from a power source device in a wirelesspower transmission system. That is, the power source device adjusts adistance enabling communication, by adjusting an output power level of acommunication channel. The power source device adjusts the distance tobe suitable for a charging pad. For example, if the output power levelof the power source device corresponds to a power 1, communication maybe performed in a region with a radius R1. In this example, the powersource device may adjust the output power level from the power 1 to apower 3, which changes the region with the radius R1 to a region with aradius R3, so that the communication may be performed in the region withthe radius R3.

For example, the power source device may be implemented in the form of apad. In this example, an antenna with a radiation pattern, and/or a chipantenna, may be used. A target device may use, for example, a flexibleprinted circuit board (FPCB) type antenna, for directivity and nearfield communication.

FIG. 19 illustrates an example of a position of a target device in awireless power transmission system. In the wireless power transmissionsystem, a source device may include a source resonator, and a targetdevice may include a target resonator. A power transferred to the targetresonator among a power transmitted via the source resonator, namely, awireless power transmission efficiency, may be measured based on aposition of the target resonator located above the source resonator, asillustrated in the example of FIG. 19 and Table 4. FIG. 19 and Table 4shows that the wireless power transmission efficiency varies based onthe position of the target resonator. For example, in positions (3) and(4), a relatively low wireless power transmission efficiency ismeasured.

TABLE 4 Position Efficiency (%) Position Efficiency (%) (1) 88.33 (8)87.02 (2) 88.84 (9) 91.07 (3) 78.25 (10) 84.65 (4) 79.79 (11) 83.68 (5)90.47 (12) 91.22 (6) 85.99 (13) 86.83 (7) 88.47 (14) 91.23 (R1) 88.17(R2) 88.73

FIG. 20 illustrates an example of a power transmission efficiency basedon a position of a target device in a wireless power transmissionsystem. In the wireless power transmission system, a source device mayinclude a source resonator, and the target device may include a targetresonator.

Referring to FIG. 20, the source device may adjust an amount of a powertransmitted via the source resonator, so that a power transferred to thetarget resonator among the power transmitted via the source resonatormay be maintained, regardless of a position of the target resonatorlocated above the source resonator. In an example in which a power valuedetected in the source device is greater than or equal to a power valueof an over protection current, the wireless power transmission system isturned off. In another example in which a reference efficiency of awireless power transmission efficiency is 50%, the source devicecontrols the transmitted power to be within a range of ±5% compared tothe reference efficiency (i.e., a power control sector), regardless ofthe position of the target resonator.

To control the power, a power tracking scheme may be used. The powertracking scheme may be used to control a supplied voltage based on anoutput power level so that an E-class power amplifier may be operated ina saturation region. A scheme of controlling the supplied voltage mayinclude a scheme of using an external SMPS, and/or a scheme of using acommercialized SMPS, and may be applied based on a used application.

FIG. 21 illustrates an example of a communication method in a wirelesspower transmission system. In operation 2101, a source deviceinitializes an SCB. The source may initialize updated system informationin the SCB to system information set at a time of manufacturing thesource device. The system information may include, for example, a serialnumber of the source device, a maximum number of target devicesaccessible to the source device, a power transmission parameter, acommunication channel parameter, and/or other information known to oneof ordinary skill in the art.

In operation 2103, the source device determines whether a start buttonis input in the source device. The source device prepares fortransmission of wireless power based on the input of the start button.The input of the start button may indicate that a target device islocated in a wireless power transmission region of the source device.

If the start button is input, in operation 2105, the source devicetransmits a wake-up power required to operate a controller of the targetdevice. Otherwise, the source device returns to operation 2103.

In operation 2107, the source device searches for communication channelsin a search order. The source device sets one of the communicationchannels to potentially be a communication channel available forcommunication with the target device.

In operation 2109, the source device detects an RSSI of the setcommunication channel, and determines whether the detected RSSI is lessthan a reference value. The RSSI indicates an intensity of aninterference signal in the communication channel affected by neighboringcommunication devices.

If the detected RSSI is greater than or equal to the reference value, inoperation 2111, the source device searches for a new channel and returnsto the operation 2107. Otherwise, in operation 2113, the source devicedetermines the set communication channel to be the communication channelavailable for communication with the target device, transmits a channelseizure signal based on a communication frequency of the setcommunication channel. The channel seizure signal may be a CW signal.The source device may continue to transmit the channel seizure signalwhile the set communication channel is used.

In operation 2115, the source device transmits an access standardinstruction. The access standard instruction may include informationused for compatibility between the source device and the target device.The access standard instruction may further include a call argument anda call parameter used to identify target devices. For example, if thesame identifying parameter as the call parameter is included in thetarget device, the target device transmits a response signal to thesource device.

In operation 2117, the source device determines whether the responsesignal (e.g., an ACK signal) is received from the target. If the ACK isnot received, in operation 2119, the source device determines whetherthe access standard instruction is transmitted a maximum number oftimes. For example, if the call argument in the access standardinstruction is set to “3”, the call parameter may include a value from“000” to “111”. In this example, the source device may transmit theaccess standard instruction eight times.

If the access standard instruction is not transmitted the maximum numberof times, in operation 2121, the source device changes the callparameter, e.g., increments the value of the call parameter. Otherwise,the source device returns to operation 2103.

If the ACK is received, in operation 2123, the source device assigns acontrol ID to the target device. The source device transmits the controlID to the target device.

FIG. 22 illustrates another example of a communication method in awireless power transmission system. In operation 2201, a target deviceinitializes an SCB. The target may initialize updated system informationin the SCB to system information used at a time of manufacturing thetarget device. The system information may include, for example, a serialnumber of the target device, a battery type, a power transmissionparameter, a communication channel parameter, and/or other informationknown to one of ordinary skill in the art.

In operation 2203, the target device searches for communication channelsin a search order. The target device sets one of communication channelsto potentially be a communication channel available for communicationwith a source device.

In operation 2205, the target device detects an RSSI of the setcommunication channel, and determines whether the detected RSSI isgreater than or equal to a reference value. The RSSI indicates anintensity of a channel seizure signal received from the source device.For example, the RSSI may indicate an intensity of a CW signal.

If the detected RSSI is less than the reference value, in operation2207, the target device searches for a new channel and returns tooperation 2203. Otherwise, in operation 2209, the target devicedetermines the set communication channel to be the communication channelavailable for communication with the source device. The target devicedetermines whether an access standard instruction is received from thesource device. The access standard instruction may include informationused for compatibility between the source device and the target device.The access standard instruction may further include a call argument anda call parameter used to identify target devices. For example, if thesame identifying parameter as a call parameter is included in the targetdevice, the target device transmits a response signal to the sourcedevice.

If the access standard instruction is not received, in operation 2211,the target device determines whether a reference time elapses. If thereference time does not elapse, the target device returns to operation2209 to wait for reception of the access standard instruction until thereference time elapses. If the reference time elapses, the target devicereturns to operation 2203 to set another one of the communicationchannels in the search order.

If the access standard instruction is received, in operation 2213, thetarget device transmits the response signal (e.g., an ACK signal) to thesource device. In operation 2215, the target device determines whether acontrol ID is received from the source device.

If the control ID is received, in operation 2217, the target devicetransmits an ACK signal to the source device. Otherwise, the targetdevice returns to operation 2215 to wait for reception of the control IDWhen the source device assigns the control ID to the target device, thesource device may call the control ID, and may request state informationof the target device.

FIG. 23 illustrates still another example of a communication apparatusin a wireless power transmission system. Referring to FIG. 23, thecommunication apparatus transmits a signal modulated in a source via acommunication transceiver 2310 and a medium access control (MAC) 2320,and receives a signal modulated in a target via the communicationtransceiver 2310 and the medium access control (MAC) 2320. Thus, thecommunication apparatus in FIG. 23 performs out-of-band communicationbetween the source and the target via the communication transceiver2310, rather than performing in-band communication through the sourceresonator 2340. A PHY controller 2330 controls an overall operationassociated with modulation of data and generation of wireless power inthe communication apparatus. A source resonator 2340, for example awireless power transmitter, transmits wireless power using mutualresonance with a target resonator (not shown).

A first demodulator 2351, for example an offset-quadrature phase-shiftkeying (O-QPSK) demodulator, performs O-QPSK demodulation. A seconddemodulator 2353, for example a chip demodulator, performs demodulationusing a pseudo-random noise (PN) sequence. A symbol demapper 2355generates a data symbol corresponding to a quadrature-phase (Q) valueand an in-phase (I) value. A decoder 2357, for example a Viterbidecoder, decodes the data symbol using a Viterbi scheme. The decoder2357 uses a Viterbi algorithm to decode an encoded bit stream receivedfrom the symbol demapper 2355 using forward error correction (FEC) basedon a convolution code. Although FIG. 23 shows the decoder 2357 as beingpart of the communication apparatus in FIG. 23, the decoder 2357 may beprovided as a separate element outside the communication apparatus ofFIG. 23.

A channel detector 2361 detects an RSSI. The RSSI is a value obtained bymeasuring a strength of an electric wave of data transferred byneighboring devices. A frame detector 2363 detects an LQI of acommunication link. The LQI is a strength between communication links,and may be calculated from the RSSI.

An encoder 2377, for example a convolution encoder, encodes an inputsignal, and outputs the encoded signal. The encoder 2377 maysuccessfully perform bit error checking using an additional bit.Although FIG. 23 shows the encoder 2377 as being part of thecommunication apparatus in FIG. 23, the encoder 2377 may be provided asa separate element outside the communication apparatus of FIG. 23. Asymbol mapper 2375 performs mapping to appropriately arrange symbolsbased on a designated modulation scheme. A second modulator 2373, forexample, a direct sequence spread spectrum (DSSS) chip modulator,spreads data to a large-scale code flow occupying a full bandwidth of acorresponding channel by multiplying a data bit by a random bit pattern,namely a pseudo-random noise (PN) sequence. Such a scheme has a goodnoise prevention performance, and provides excellent security becausethe spread data is very difficult to recover without knowing thepseudo-random noise (PN) sequence. A first modulator 2371, for examplean O-QPSK modulator, performs O-QPSK modulation.

A protection unit 2387 prevents an overcurrent from being supplied to apower amplifier 2385. The power amplifier 2385 generates power requiredby the target. A detector 2383 detects a change in impedance of thetarget. Additionally, the detector 2383 may detect power input to thepower amplifier 2385. A tracking unit 2381 tracks matching impedancebetween the source and the target. Additionally, the tracking unit 2381may track a resonant frequency between the source and the target.

In the following description, the term “resonator” used in thediscussion of FIGS. 24A through 26B refers to both a source resonatorand a target resonator.

FIGS. 24A and 24B illustrate examples of a distribution of a magneticfield in a feeder and a resonator of a wireless power transmitter. Whena resonator receives power supplied through a separate feeder, magneticfields are formed in both the feeder and the resonator.

FIG. 24A illustrates an example of a structure of a wireless powertransmitter in which a feeder 2410 and a resonator 2420 do not have acommon ground. Referring to FIG. 24A, as an input current flows into afeeder 2410 through a terminal labeled “+” and out of the feeder 2410through a terminal labeled “−”, a magnetic field 2430 is formed by theinput current. A direction 2431 of the magnetic field 2430 inside thefeeder 2410 is into the plane of FIG. 24A, and has a phase that isopposite to a phase of a direction 2433 of the magnetic field 2430outside the feeder 2410. The magnetic field 2430 formed by the feeder2410 induces a current to flow in a resonator 2420. The direction of theinduced current in the resonator 2420 is opposite to a direction of theinput current in the feeder 2410 as indicated by the dashed arrows inFIG. 24A.

The induced current in the resonator 2420 forms a magnetic field 2440.Directions of the magnetic field 2440 are the same at all positionsinside the resonator 2420. Accordingly, a direction 2441 of the magneticfield 2440 formed by the resonator 2420 inside the feeder 2410 has thesame phase as a direction 2443 of the magnetic field 2440 formed by theresonator 2420 outside the feeder 2410.

Consequently, when the magnetic field 2430 formed by the feeder 2410 andthe magnetic field 2440 formed by the resonator 2420 are combined, astrength of the total magnetic field inside the resonator 2420 decreasesinside the feeder 2410 and increases outside the feeder 2410. In anexample in which power is supplied to the resonator 2420 through thefeeder 2410 configured as illustrated in FIG. 24A, the strength of thetotal magnetic field decreases in the center of the resonator 2420, butincreases outside the resonator 2420. In another example in which amagnetic field is randomly distributed in the resonator 2420, it isdifficult to perform impedance matching since an input impedance willfrequently vary. Additionally, when the strength of the total magneticfield increases, an efficiency of wireless power transmission increases.Conversely, when the strength of the total magnetic field is decreases,the efficiency of wireless power transmission decreases. Accordingly,the power transmission efficiency may be reduced on average.

FIG. 24B illustrates an example of a structure of a wireless powertransmitter in which a resonator 2450 and a feeder 2460 have a commonground. The resonator 2450 includes a capacitor 2451. The feeder 2460receives a radio frequency (RF) signal via a port 2461. When the RFsignal is input to the feeder 2460, an input current is generated in thefeeder 2460. The input current flowing in the feeder 2460 forms amagnetic field, and a current is induced in the resonator 2450 by themagnetic field. Additionally, another magnetic field is formed by theinduced current flowing in the resonator 2450. In this example, adirection of the input current flowing in the feeder 2460 has a phaseopposite to a phase of a direction of the induced current flowing in theresonator 2450. Accordingly, in a region between the resonator 2450 andthe feeder 2460, a direction 2471 of the magnetic field formed by theinput current has the same phase as a direction 2473 of the magneticfield formed by the induced current, and thus the strength of the totalmagnetic field increases in the region between the resonator 2450 andthe feeder 2460. Conversely, inside the feeder 2460, a direction 2481 ofthe magnetic field formed by the input current has a phase opposite to aphase of a direction 2483 of the magnetic field formed by the inducedcurrent, and thus the strength of the total magnetic field decreasesinside the feeder 2460. Therefore, the strength of the total magneticfield decreases in the center of the resonator 2450, but increasesoutside the resonator 2450.

An input impedance may be adjusted by adjusting an internal area of thefeeder 2460. The input impedance refers to an impedance viewed in adirection from the feeder 2460 to the resonator 2450. When the internalarea of the feeder 2460 is increased, the input impedance is increased.Conversely, when the internal area of the feeder 2460 is decreased, theinput impedance is decreased. Because the magnetic field is randomlydistributed in the resonator 2450 despite a reduction in the inputimpedance, a value of the input impedance may vary based on a locationof a target device. Accordingly, a separate matching network may berequired to match the input impedance to an output impedance of a poweramplifier. For example, when the input impedance is increased, aseparate matching network may be used to match the increased inputimpedance to a relatively low output impedance of the power amplifier.

FIGS. 25A and 25B illustrate an example of a wireless power transmitterincluding a resonator and a feeding unit. Referring to FIG. 25A, thewireless power transmitter includes a resonator 2510 and a feeding unit2520. The resonator 2510 further includes a capacitor 2511. The feedingunit 2520 is electrically connected to both ends of the capacitor 2511.

FIG. 25B illustrates, in greater detail, a structure of the wirelesspower transmitter of FIG. 25A. The resonator 2510 includes a firsttransmission line (not identified by a reference numeral in FIG. 25B,but formed by various elements in FIG. 25B as discussed below), a firstconductor 2541, a second conductor 2542, and at least one capacitor2550.

The capacitor 2550 is inserted in series between a first signalconducting portion 2531 and a second signal conducting portion 2532,causing an electric field to be confined within the capacitor 2550.Generally, a transmission line includes at least one conductor in anupper portion of the transmission line, and at least one conductor in alower portion of first transmission line. A current may flow through theat least one conductor disposed in the upper portion of the firsttransmission line, and the at least one conductor disposed in the lowerportion of the first transmission line may be electrically grounded. Inthis example, a conductor disposed in an upper portion of the firsttransmission line in FIG. 25B is separated into two portions that willbe referred to as the first signal conducting portion 2531 and thesecond signal conducting portion 2532. A conductor disposed in a lowerportion of the first transmission line in FIG. 25B will be referred toas a first ground conducting portion 2533.

As illustrated in FIG. 25B, the resonator 2510 has a generallytwo-dimensional (2D) structure. The first transmission line includes thefirst signal conducting portion 2531 and the second signal conductingportion 2532 in the upper portion of the first transmission line, andincludes the first ground conducting portion 2533 in the lower portionof the first transmission line. The first signal conducting portion 2531and the second signal conducting portion 2532 are disposed to face thefirst ground conducting portion 2533. A current flows through the firstsignal conducting portion 2531 and the second signal conducting portion2532.

One end of the first signal conducting portion 2531 is connected to oneend of the first conductor 2541, the other end of the first signalconducting portion 2531 is connected to the capacitor 2550, and theother end of the first conductor 2541 is connected to one end of thefirst ground conducting portion 2533. One end of the second signalconducting portion 2532 is connected to one end of the second conductor2542, the other end of the second signal conducting portion 2532 isconnected to the other end of the capacitor 2550, and the other end ofthe second conductor 2542 is connected to the other end of the groundconducting portion 2533. Accordingly, the first signal conductingportion 2531, the second signal conducting portion 2532, the firstground conducting portion 2533, the first conductor 2541, and the secondconductor 2542 are connected to each other, causing the resonator 2510to have an electrically closed loop structure. The term “loop structure”includes a polygonal structure, a circular structure, a rectangularstructure, and any other geometrical structure that is closed, i.e.,that does not have any opening in its perimeter. The expression “havinga loop structure” indicates a structure that is electrically closed.

The capacitor 2550 is inserted into an intermediate portion of the firsttransmission line. In the example in FIG. 25B, the capacitor 2550 isinserted into a space between the first signal conducting portion 2531and the second signal conducting portion 2532. The capacitor 2550 may bea lumped element capacitor, a distributed capacitor, or any other typeof capacitor known to one of ordinary skill in the art. For example, adistributed element capacitor may include a zigzagged conductor line anda dielectric material having a relatively high permittivity disposedbetween parallel portions of the zigzagged conductor line.

The capacitor 2550 inserted into the first transmission line may causethe resonator 2510 to have a characteristic of a metamaterial. Ametamaterial is a material having a predetermined electrical propertythat is not found in nature, and thus may have an artificially designedstructure. All materials existing in nature have a magnetic permeabilityand permittivity. Most materials have a positive magnetic permeabilityand/or a positive permittivity.

For most materials, a right-hand rule may be applied to an electricfield, a magnetic field, and a Poynting vector of the materials, so thematerials may be referred to as right-handed materials (RHMs). However,a metamaterial that has a magnetic permeability and/or a permittivitythat is not found in nature, and may be classified into an epsilonnegative (ENG) material, a mu negative (MNG) material, a double negative(DNG) material, a negative refractive index (NRI) material, aleft-handed (LH) material, and other metamaterial classifications knownto one of ordinary skill in the art based on a sign of the magneticpermeability of the metamaterial and a sign of the permittivity of themetamaterial.

If the capacitor 2550 is a lumped element capacitor and a capacitance ofthe capacitor 2550 is appropriately determined, the resonator 2510 mayhave a characteristic of a metamaterial. If the resonator 2510 is causedto have a negative magnetic permeability by appropriately adjusting thecapacitance of the capacitor 2550, the resonator 2510 may also bereferred to as an MNG resonator. Various criteria may be applied todetermine the capacitance of the capacitor 2550. For example, thevarious criteria may include a criterion for enabling the resonator 2510to have the characteristic of the metamaterial, a criterion for enablingthe resonator 2510 to have a negative magnetic permeability at a targetfrequency, a criterion for enabling the resonator 2510 to have a zerothorder resonance characteristic at the target frequency, and any othersuitable criterion. Based on any one or any combination of theaforementioned criteria, the capacitance of the capacitor 2550 may beappropriately determined.

The resonator 2510, hereinafter referred to as the MNG resonator 2510,may have a zeroth order resonance characteristic of having a resonantfrequency when a propagation constant is “0”. If the MNG resonator 2510has the zeroth order resonance characteristic, the resonant frequency isindependent of a physical size of the MNG resonator 2510. By changingthe capacitance of the capacitor 2550, the resonant frequency of the MNGresonator 2510 may be changed without changing the physical size of theMNG resonator 2510.

In a near field, the electric field is concentrated in the capacitor2550 inserted into the first transmission line, causing the magneticfield to become dominant in the near field. The MNG resonator 2510 has arelatively high Q-factor when the capacitor 2550 is a lumped element,thereby increasing a power transmission efficiency. The Q-factorindicates a level of an ohmic loss or a ratio of a reactance withrespect to a resistance in the wireless power transmission. As will beunderstood by one of ordinary skill in the art, the efficiency of thewireless power transmission will increase as the Q-factor increases.

Although not illustrated in FIG. 25B, a magnetic core passing throughthe MNG resonator 2510 may be provided to increase a power transmissiondistance.

Referring to FIG. 25B, the feeding unit 2520 includes a secondtransmission line (not identified by a reference numeral in FIG. 25B,but formed by various elements in FIG. 25B as discussed below), a thirdconductor 2571, a fourth conductor 2572, a fifth conductor 2581, and asixth conductor 2582.

The second transmission line includes a third signal conducting portion2561 and a fourth signal conducting portion 2562 in an upper portion ofthe second transmission line, and includes a second ground conductingportion 2563 in a lower portion of the second transmission line. Thethird signal conducting portion 2561 and the fourth signal conductingportion 2562 are disposed to face the second ground conducting portion2563. A current flows through the third signal conducting portion 2561and the fourth signal conducting portion 2562.

One end of the third signal conducting portion 2561 is connected to oneend of the third conductor 2571, the other end of the third signalconducting portion 2561 is connected to one end of the fifth conductor2581, and the other end of the third conductor 2571 is connected to oneend of the second ground conducting portion 2563. One end of the fourthsignal conducting portion 2562 is connected to one end of the fourthconductor 2572, the other end of the fourth signal conducting portion2562 is connected to one end the sixth conductor 2582, and the other endof the fourth conductor 2572 is connected to the other end of the secondground conducting portion 2563. The other end of the fifth conductor2581 is connected to the first signal conducting portion 2531 at or nearwhere the first signal conducting portion 2531 is connected to one endof the capacitor 2550, and the other end of the sixth conductor 2582 isconnected to the second signal conducting portion 2532 at or near wherethe second signal conducting portion 2532 is connected to the other endof the capacitor 2550. Thus, the fifth conductor 2581 and the sixthconductor 2582 are connected in parallel to both ends of the capacitor2550. The fifth conductor 2581 and the sixth conductor 2582 are used asan input port to receive an RF signal as an input.

Accordingly, the third signal conducting portion 2561, the fourth signalconducting portion 2562, the second ground conducting portion 2563, thethird conductor 2571, the fourth conductor 2572, the fifth conductor2581, the sixth conductor 2582, and the resonator 2510 are connected toeach other, causing the resonator 2510 and the feeding unit 2520 to havean electrically closed loop structure. The term “loop structure”includes a polygonal structure, a circular structure, a rectangularstructure, and any other geometrical structure that is closed, i.e.,that does not have any opening in its perimeter. The expression “havinga loop structure” indicates a structure that is electrically closed.

If an RF signal is input to the fifth conductor 2581 or the sixthconductor 2582, input current flows through the feeding unit 2520 andthe resonator 2510, generating a magnetic field that induces a currentin the resonator 2510. A direction of the input current flowing throughthe feeding unit 2520 is identical to a direction of the induced currentflowing through the resonator 2510, thereby causing a strength of atotal magnetic field to increase in the center of the resonator 2510,and decrease near the outer periphery of the resonator 2510.

An input impedance is determined by an area of a region between theresonator 2510 and the feeding unit 2520. Accordingly, a separatematching network used to match the input impedance to an outputimpedance of a power amplifier may not be necessary. However, if amatching network is used, the input impedance may be adjusted byadjusting a size of the feeding unit 2520, and accordingly a structureof the matching network may be simplified. The simplified structure ofthe matching network may reduce a matching loss of the matching network.

The second transmission line, the third conductor 2571, the fourthconductor 2572, the fifth conductor 2581, and the sixth conductor 2582of the feeding unit may have a structure identical to the structure ofthe resonator 2510. For example, if the resonator 2510 has a loopstructure, the feeding unit 2520 may also have a loop structure. Asanother example, if the resonator 2510 has a circular structure, thefeeding unit 2520 may also have a circular structure.

FIG. 26A illustrates an example of a distribution of a magnetic fieldinside a resonator produced by feeding of a feeding unit. FIG. 26A moresimply illustrates the resonator 2510 and the feeding unit 2520 of FIGS.25A and 25B, and the names of the various elements in FIG. 25B will beused in the following description of FIG. 26A without referencenumerals.

A feeding operation may be an operation of supplying power to a sourceresonator in wireless power transmission, or an operation of supplyingAC power to a rectification unit in wireless power transmission. FIG.26A illustrates a direction of input current flowing in the feedingunit, and a direction of induced current flowing in the sourceresonator. Additionally, FIG. 26A illustrates a direction of a magneticfield formed by the input current of the feeding unit, and a directionof a magnetic field formed by the induced current of the sourceresonator.

Referring to FIG. 26A, the fifth conductor or the sixth conductor of thefeeding unit 2520 may be used as an input port 2610. In FIG. 26A, thesixth conductor of the feeding unit is being used as the input port2610. An RF signal is input to the input port 2610. The RF signal may beoutput from a power amplifier. The power amplifier may increase anddecrease an amplitude of the RF signal based on a power requirement of atarget device. The RF signal input to the input port 2610 is representedin FIG. 26A as an input current flowing in the feeding unit. The inputcurrent flows in a clockwise direction in the feeding unit along thesecond transmission line of the feeding unit. The fifth conductor andthe sixth conductor of the feeding unit are electrically connected tothe resonator. More specifically, the fifth conductor of the feedingunit is connected to the first signal conducting portion of theresonator, and the sixth conductor of the feeding unit is connected tothe second signal conducting portion of the resonator. Accordingly, theinput current flows in both the resonator and the feeding unit. Theinput current flows in a counterclockwise direction in the resonatoralong the first transmission line of the resonator. The input currentflowing in the resonator generates a magnetic field, and the magneticfield induces a current in the resonator due to the magnetic field. Theinduced current flows in a clockwise direction in the resonator alongthe first transmission line of the resonator. The induced current in theresonator transfers energy to the capacitor of the resonator, and alsogenerates a magnetic field. In FIG. 26A, the input current flowing inthe feeding unit and the resonator is indicated by solid lines witharrowheads, and the induced current flowing in the resonator isindicated by dashed lines with arrowheads.

A direction of a magnetic field generated by a current is determinedbased on the right-hand rule. As illustrated in FIG. 26A, within thefeeding unit, a direction 2621 of the magnetic field generated by theinput current flowing in the feeding unit is identical to a direction2623 of the magnetic field generated by the induced current flowing inthe resonator. Accordingly, a strength of the total magnetic field mayincreases inside the feeding unit.

In contrast, as illustrated in FIG. 26A, in a region between the feedingunit and the resonator, a direction 2633 of the magnetic field generatedby the input current flowing in the feeding unit is opposite to adirection 2631 of the magnetic field generated by the induced currentflowing in the source resonator. Accordingly, the strength of the totalmagnetic field decreases in the region between the feeding unit and theresonator.

Typically, in a resonator having a loop structure, a strength of amagnetic field decreases in the center of the resonator, and increasesnear an outer periphery of the resonator. However, referring to FIG.26A, since the feeding unit is electrically connected to both ends ofthe capacitor of the resonator, the direction of the induced current inthe resonator is identical to the direction of the input current in thefeeding unit. Since the direction of the induced current in theresonator is identical to the direction of the input current in thefeeding unit, the strength of the total magnetic field increases insidethe feeding unit, and decreases outside the feeding unit. As a result,due to the feeding unit, the strength of the total magnetic fieldincreases in the center of the resonator having the loop structure, anddecreases near an outer periphery of the resonator, thereby compensatingfor the normal characteristic of the resonator having the loop structurein which the strength of the magnetic field decreases in the center ofthe resonator, and increases near the outer periphery of the resonator.Thus, the strength of the total magnetic field may be constant insidethe resonator.

A power transmission efficiency for transferring wireless power from asource resonator to a target resonator is proportional to the strengthof the total magnetic field generated in the source resonator.Accordingly, when the strength of the total magnetic field increasesinside the source resonator, the power transmission efficiency alsoincreases.

FIG. 26B illustrates examples of equivalent circuits of a feeding unitand a resonator. Referring to FIG. 26B, a feeding unit 2640 and aresonator 2650 may be represented by the equivalent circuits in FIG.26B. The feeding unit 2640 is represented as an inductor having aninductance L_(f), and the resonator 2650 is represented as a seriesconnection of an inductor having an inductance L coupled to theinductance L_(f) of the feeding unit 2640 by a mutual inductance M, acapacitor having a capacitance C, and a resistor having a resistance R.An example of an input impedance Z_(in) viewed in a direction from thefeeding unit 2640 to the resonator 2650 may be expressed by thefollowing Equation 4:

$\begin{matrix}{Z_{in} = \frac{\left( {\omega\; M} \right)^{2}}{Z}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In Equation 4, M denotes a mutual inductance between the feeding unit2640 and the resonator 2650, ω denotes a resonant frequency of thefeeding unit 2640 and the resonator 2650, and Z denotes an impedanceviewed in a direction from the resonator 2650 to a target device. As canbe seen from Equation 4, the input impedance Z_(in) is proportional tothe square of the mutual inductance M. Accordingly, the input impedanceZ_(in) may be adjusted by adjusting the mutual inductance M. The mutualinductance M depends on an area of a region between the feeding unit2640 and the resonator 2650. The area of the region between the feedingunit 2640 and the resonator 2650 may be adjusted by adjusting a size ofthe feeding unit 2640, thereby adjusting the mutual inductance M and theinput impedance Z_(in). Since the input impedance Z_(in) may be adjustedby adjusting the size of the feeding unit 2640, it may be unnecessary touse a separate matching network to perform impedance matching with anoutput impedance of a power amplifier.

In a target resonator and a feeding unit included in a wireless powerreceiver, a magnetic field may be distributed as illustrated in FIG.26A. For example, the target resonator may receive wireless power from asource resonator via magnetic coupling. The received wireless powerinduces a current in the target resonator. The induced current in thetarget resonator generates a magnetic field, which induces a current inthe feeding unit. If the target resonator is connected to the feedingunit as illustrated in FIG. 26A, a direction of the induced currentflowing in the target resonator will be identical to a direction of theinduced current flowing in the feeding unit. Accordingly, for thereasons discussed above in connection with FIG. 26A, a strength of thetotal magnetic field will increase inside the feeding unit, and willdecrease in a region between the feeding unit and the target resonator.

FIG. 27 is a diagram illustrating an example of an electric vehiclecharging system. Referring to FIG. 27, an electric vehicle chargingsystem 2700 includes a source system 2710, a source resonator 2720, atarget resonator 2730, a target system 2740, and an electric vehiclebattery 2750.

In one example, the electric vehicle charging system 2700 has astructure similar to the structure of the wireless power transmissionand charging system of FIG. 1. The source system 2710 and the sourceresonator 2720 in the electric vehicle charging system 2700 operate as asource. The target resonator 2730 and the target system 2740 in theelectric vehicle charging system 2700 operate as a target.

In one example, the source system 2710 includes an alternatingcurrent-to-direct current (AC/DC) converter, a power detector, a powerconverter, a control and communication (control/communication) unitsimilar to those of the source device 110 of FIG. 1. In one example, thetarget system 2740 includes a rectification unit, a DC-to-DC (DC/DC)converter, a switch unit, a charging unit, and a control/communicationunit similar to those of the target device 120 of FIG. 1. The electricvehicle battery 2750 is charged by the target system 2740. The electricvehicle charging system 2700 may use a resonant frequency in a band of afew kHz to tens of MHz.

The source system 2710 generates power based on a type of the vehiclebeing charged, a capacity of the electric vehicle battery 2750, and acharging state of the electric vehicle battery 2750, and wirelesslytransmits the generated power to the target system 2740 via a magneticcoupling between the source resonator 2720 and the target resonator2730.

The source system 2710 may control an alignment of the source resonator2720 and the target resonator 2730. For example, when the sourceresonator 2720 and the target resonator 2730 are not aligned, thecontroller of the source system 2710 may transmit a message to thetarget system 2740 to control the alignment of the source resonator 2720and the target resonator 2730.

For example, when the target resonator 2730 is not located in a positionenabling maximum magnetic coupling, the source resonator 2720 and thetarget resonator 2730 are not properly aligned. When a vehicle does notstop at a proper position to accurately align the source resonator 2720and the target resonator 2730, the source system 2710 may instruct aposition of the vehicle to be adjusted to control the source resonator2720 and the target resonator 2730 to be aligned. However, this is justan example, and other methods of aligning the source resonator 2720 andthe target resonator 2730 may be used.

The source system 2710 and the target system 2740 may transmit orreceive an ID of a vehicle and exchange various messages by performingcommunication with each other.

The descriptions of FIGS. 2 through 26B are also applicable to theelectric vehicle charging system 2700. However, the electric vehiclecharging system 2700 may use a resonant frequency in a band of a few kHzto tens of MHz, and may wirelessly transmit power that is equal to orhigher than tens of watts to charge the electric vehicle battery 2750.

According to the teachings above, there is provided a wireless powertransmission system including a source that selects a channel withlittle interference by neighboring communication devices, from amongchannels available for communication, and that transmits a channelseizure signal with a predetermined intensity. When an intensity of thechannel seizure signal is greater than a reference value, a target maydetermine a channel corresponding to the channel seizure signal, to be acommunication channel. Thus, it is possible to prevent the target fromincorrectly accessing the source.

Additionally, according to various examples, in a wireless powertransmission system, a source may transmit an access standardinstruction, and a target may transmit a response signal only when areference requested by the access standard instruction is satisfied.Thus, it is possible to prevent a plurality of targets from collidingwith each other.

Furthermore, according to various examples, in a wireless powertransmission system, a source may compare power used to transmit aninstruction via a communication channel, with power received by atarget, and may determine whether the target incorrectly accesses thesource. Moreover, according to various examples, in a wireless powertransmission system, a source may compare wirelessly transmitted powerwith power transferred to a load of a target, in a charging mode, andmay determine whether the target incorrectly accesses the source.

The units described herein may be implemented using hardware componentsand software components. For example, the hardware components mayinclude microphones, amplifiers, band-pass filters, audio to digitalconvertors, and processing devices. A processing device may beimplemented using one or more general-purpose or special purposecomputers, such as, for example, a processor, a controller and anarithmetic logic unit, a digital signal processor, a microcomputer, afield programmable array, a programmable logic unit, a microprocessor orany other device capable of responding to and executing instructions ina defined manner. The processing device may run an operating system (OS)and one or more software applications that run on the OS. The processingdevice also may access, store, manipulate, process, and create data inresponse to execution of the software. For purpose of simplicity, thedescription of a processing device is used as singular; however, oneskilled in the art will appreciated that a processing device may includemultiple processing elements and multiple types of processing elements.For example, a processing device may include multiple processors or aprocessor and a controller. In addition, different processingconfigurations are possible, such a parallel processors.

The software may include a computer program, a piece of code, aninstruction, or some combination thereof, to independently orcollectively instruct or configure the processing device to operate asdesired. Software and data may be embodied permanently or temporarily inany type of machine, component, physical or virtual equipment, computerstorage medium or device, or in a propagated signal wave capable ofproviding instructions or data to or being interpreted by the processingdevice. The software also may be distributed over network coupledcomputer systems so that the software is stored and executed in adistributed fashion. For example, the software and data may be stored byone or more computer readable recording mediums. The computer readablerecording medium may include any data storage device that can store datawhich can be thereafter read by a computer system or processing device.Examples of the non-transitory computer readable recording mediuminclude read-only memory (ROM), random-access memory (RAM), CD-ROMs,magnetic tapes, floppy disks, optical data storage devices. Also,functional programs, codes, and code segments accomplishing the examplesdisclosed herein can be easily construed by programmers skilled in theart to which the examples pertain based on and using the flow diagramsand block diagrams of the figures and their corresponding descriptionsas provided herein.

As a non-exhaustive illustration only, a terminal or device describedherein may refer to mobile devices such as a cellular phone, a personaldigital assistant (PDA), a digital camera, a portable game console, andan MP3 player, a portable/personal multimedia player (PMP), a handhelde-book, a portable laptop PC, a global positioning system (GPS)navigation, a tablet, a sensor, and devices such as a desktop PC, a highdefinition television (HDTV), an optical disc player, a setup box, ahome appliance, and the like that are capable of wireless communicationor network communication consistent with that which is disclosed herein.

A number of examples have been described above. Nevertheless, it will beunderstood that various modifications may be made. For example, suitableresults may be achieved if the described techniques are performed in adifferent order and/or if components in a described system,architecture, device, or circuit are combined in a different mannerand/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

What is claimed is:
 1. A communication apparatus in a wireless powertransmission system, the communication apparatus comprising: a channelsearch unit configured to search for communication channels other than achannel used in wireless power transmission, and measure stateinformation of the communication channels; a channel determining unitconfigured to determine a communication channel available forcommunication with a target device based on the measured stateinformation; a communication unit configured to transmit an accessinstruction to the target device using the determined communicationchannel; and a controller configured to determine whether to communicatewith the target device using the determined communication channel basedon whether a response signal corresponding to the access instruction isreceived.
 2. The communication apparatus of claim 1, wherein thecommunication apparatus is configured to: detect the target device in awireless power transmission region of the communication apparatus. 3.The communication apparatus of claim 1, wherein the channel search unitcomprises: a channel measuring unit configured to measure intensities ofinterference signals of the respective communication channels.
 4. Thecommunication apparatus of claim 3, wherein the channel measuring unitis further configured to: measure the intensities for a predeterminedperiod of time.
 5. The communication apparatus of claim 3, wherein thechannel determining unit is further configured to: determine acommunication channel comprising an intensity of an interference signalthat is less than or equal to a predetermined value, among the measuredintensities, to be the communication channel available for communicationwith the target device.
 6. The communication apparatus of claim 3,wherein the channel determining unit is further configured to: determinea communication channel comprising an intensity of an interferencesignal that is lowest in value, among the measured intensities, to bethe communication channel available for communication with the targetdevice if each of the intensities are greater than or equal to a channelselection reference level.
 7. The communication apparatus of claim 1,wherein the communication unit is further configured to: transmit achannel seizure signal to the target device, the channel seizure signalcomprising a predetermined intensity.
 8. The communication apparatus ofclaim 7, wherein the channel seizure signal is a continuous wave (CW)signal comprising a predetermined intensity and a power greater than acommunication signal of a direct-sequence spread spectrum (DSSS).
 9. Thecommunication apparatus of claim 1, wherein the controller is furtherconfigured to: assign a control identifier (ID) to the target device ifthe response signal is received.
 10. The communication apparatus ofclaim 1, wherein the communication unit is further configured to:transmit a signal to request information on a power required by thetarget device using a communication frequency of the determinedcommunication channel.
 11. The communication apparatus of claim 10,wherein the controller is further configured to: determine an amount ofa wireless power to be transmitted by the communication apparatus basedon the information regarding the power required by the target device;and control a wireless power output from the communication apparatusbased on the determined amount of the wireless power.
 12. Thecommunication apparatus of claim 1, wherein the channel search unit isfurther configured to: search for the communication channels based on asearch table set based on a type of the communication apparatus, or aunique ID assigned to the communication apparatus.
 13. The communicationapparatus of claim 1, wherein the controller is further configured to:control the channel search unit to search for the communicationchannels, regardless of whether the target device is waked up.
 14. Thecommunication apparatus of claim 1, wherein the controller is furtherconfigured to: determine whether the communication apparatus is accessedby the target device based on information on a power of a communicationoutput of the communication apparatus in the determined communicationchannel, and information on a power of the communication output receivedby the target device.
 15. The communication apparatus of claim 14,wherein the controller is further configured to: control the channelsearch unit to search for the communication channels based on a channelsearch start command if the communication apparatus is not accessed bythe target device; and control the channel search unit to search for thecommunication channels based on an amount of a change in a currentoutput from the communication apparatus if the communication apparatusis accessed by the target device.
 16. The communication apparatus ofclaim 1, wherein the controller is further configured to: determine adifference between a wireless power transmitted by the communicationapparatus and a power transferred to a load of the target device; anddetermine whether the target device incorrectly accesses thecommunication apparatus based on the determined difference.
 17. Thecommunication apparatus of claim 1, wherein the controller is furtherconfigured to: determine a difference between a time in which an amountof a wireless power transmitted by the communication apparatus ischanged to a predetermined value, and a time in which an amount of apower transferred to a load of the target device is changed; anddetermine whether the target device incorrectly accesses thecommunication apparatus based on the determined difference.
 18. Thecommunication apparatus of claim 1, wherein the controller is furtherconfigured to: determine a power of a communication output in thedetermined communication channel based on a table to which an intensityof an interference signal in the determined communication channel, and apower of an output signal required to transmit data within apredetermined error range, are mapped.
 19. The communication apparatusof claim 1, wherein the controller is further configured to: determine atime required to measure intensities of interference signals of therespective communication channels.
 20. The communication apparatus ofclaim 1, wherein the controller is further configured to: determine tochange the determined communication channel to another communicationchannel if an error in the determined communication channel between thecommunication apparatus and the target device is greater than apredetermined value, or if an intensity of an interference signal of thedetermined communication channel is greater than a predetermined value;and transmit a channel change request instruction to the target device.21. A communication apparatus in a wireless power transmission system,the communication apparatus comprising: a channel search unit configuredto search for communication channels other than a channel used inwireless power transmission, and measure state information of thecommunication channels; a channel determining unit configured todetermine a communication channel available for communication with asource device based on the measured state information; and a controllerconfigured to determine whether to communicate with the source deviceusing the determined communication channel based on whether an accessinstruction is received from the source device using the determinedcommunication channel.
 22. The communication apparatus of claim 21,wherein the controller is configured to: determine whether the accessinstruction is received from the source device using the determinedcommunication channel within a reference time.
 23. The communicationapparatus of claim 22, further comprising: a communication unitconfigured to transmit, to the source device, a response signalcorresponding to the access instruction if the access instruction isreceived within the reference time.
 24. The communication apparatus ofclaim 23, wherein the communication unit is further configured to:receive, from the source device, a control ID assigned to thecommunication apparatus and that corresponds to the response signal. 25.The communication apparatus of claim 22, wherein the channel search unitis further configured to: search for another communication channel, andmeasure state information of the other communication channel, if theaccess instruction is not received within the reference time.
 26. Thecommunication apparatus of claim 21, wherein: the channel search unit isfurther configured to measure intensities of channel seizure signals ofthe respective communication channels that are transmitted by the sourcedevice; and the channel determining unit is further configured todetermine a communication channel comprising an intensity of a channelseizure signal that is greater than a predetermined value, among theintensities, to be the communication channel available for communicationwith the source device.
 27. The communication apparatus of claim 26,wherein the channel seizure signal is a continuous wave (CW) signalcomprising a predetermined intensity and a power greater than acommunication signal of a direct-sequence spread spectrum (DSSS). 28.The communication apparatus of claim 21, wherein: the communicationapparatus is configured to receive channel seizure signals from sourcedevices; and the controller is further configured to select one of thesource devices using a communication channel comprising an intensity ofa channel seizure signal that is greatest in value, from among thesource devices, and determine to receive a wireless power from theselected one of the source devices.
 29. The communication apparatus ofclaim 28, wherein the channel determining unit is further configured to:determine the communication channel used by the selected one of thesource devices to be a communication channel available for communicationwith the selected one of the source devices.
 30. The communicationapparatus of claim 21, wherein the channel search unit is furtherconfigured to: search for the communication channels based on a searchtable set based on a type of the communication apparatus, or a unique IDassigned to the communication apparatus.
 31. The communication apparatusof claim 21, further comprising: a direct current (DC)-to-DC (DC/DC)converter; and a load, wherein the controller is further configured todetermine a power required by the communication apparatus based on apower measured at an input end of the DC/DC converter, a power measuredat an output end of the DC/DC converter, and a power transferred to theload.
 32. A communication method in a wireless power transmissionsystem, the communication method comprising: searching for communicationchannels other than a channel used in wireless power transmission;measuring state information of the communication channels; determining acommunication channel available for communication with a target devicebased on the measured state information; transmitting an accessinstruction to the target device using the determined communicationchannel; and determining whether to communicate with the target deviceusing the determined communication channel based on whether a responsesignal corresponding to the access instruction is received.
 33. Thecommunication method of 32, further comprising: transmitting a channelseizure signal to the target device, the channel seizure signalcomprising a predetermined intensity.
 34. The communication method ofclaim 32, wherein the measuring of the state information comprises:measuring intensities of interference signals of the respectivecommunication channels.
 35. The communication method of claim 34,wherein the determining of the communication channel comprises:determining a communication channel comprising an intensity of aninterference signal that is less than or equal to a predetermined value,among the measured intensities, to be the communication channelavailable for communication with the target device.
 36. A communicationmethod in a wireless power transmission system, the communication methodcomprising: searching for communication channels other than a channelused in wireless power transmission; measuring state information of thecommunication channels; determining a communication channel availablefor communication with a source device based on the measured stateinformation; and determining whether to communicate with the sourcedevice using the determined communication channel based on whether anaccess instruction is received from the source device using thedetermined communication channel.